| /* |
| * Fast Userspace Mutexes (which I call "Futexes!"). |
| * (C) Rusty Russell, IBM 2002 |
| * |
| * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar |
| * (C) Copyright 2003 Red Hat Inc, All Rights Reserved |
| * |
| * Removed page pinning, fix privately mapped COW pages and other cleanups |
| * (C) Copyright 2003, 2004 Jamie Lokier |
| * |
| * Robust futex support started by Ingo Molnar |
| * (C) Copyright 2006 Red Hat Inc, All Rights Reserved |
| * Thanks to Thomas Gleixner for suggestions, analysis and fixes. |
| * |
| * PI-futex support started by Ingo Molnar and Thomas Gleixner |
| * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
| * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> |
| * |
| * PRIVATE futexes by Eric Dumazet |
| * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> |
| * |
| * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> |
| * Copyright (C) IBM Corporation, 2009 |
| * Thanks to Thomas Gleixner for conceptual design and careful reviews. |
| * |
| * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly |
| * enough at me, Linus for the original (flawed) idea, Matthew |
| * Kirkwood for proof-of-concept implementation. |
| * |
| * "The futexes are also cursed." |
| * "But they come in a choice of three flavours!" |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 2 of the License, or |
| * (at your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, write to the Free Software |
| * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
| */ |
| #include <linux/slab.h> |
| #include <linux/poll.h> |
| #include <linux/fs.h> |
| #include <linux/file.h> |
| #include <linux/jhash.h> |
| #include <linux/init.h> |
| #include <linux/futex.h> |
| #include <linux/mount.h> |
| #include <linux/pagemap.h> |
| #include <linux/syscalls.h> |
| #include <linux/signal.h> |
| #include <linux/export.h> |
| #include <linux/magic.h> |
| #include <linux/pid.h> |
| #include <linux/nsproxy.h> |
| #include <linux/ptrace.h> |
| #include <linux/sched/rt.h> |
| #include <linux/hugetlb.h> |
| #include <linux/freezer.h> |
| #include <linux/bootmem.h> |
| #include <linux/fault-inject.h> |
| |
| #include <asm/futex.h> |
| |
| #include "locking/rtmutex_common.h" |
| |
| /* |
| * READ this before attempting to hack on futexes! |
| * |
| * Basic futex operation and ordering guarantees |
| * ============================================= |
| * |
| * The waiter reads the futex value in user space and calls |
| * futex_wait(). This function computes the hash bucket and acquires |
| * the hash bucket lock. After that it reads the futex user space value |
| * again and verifies that the data has not changed. If it has not changed |
| * it enqueues itself into the hash bucket, releases the hash bucket lock |
| * and schedules. |
| * |
| * The waker side modifies the user space value of the futex and calls |
| * futex_wake(). This function computes the hash bucket and acquires the |
| * hash bucket lock. Then it looks for waiters on that futex in the hash |
| * bucket and wakes them. |
| * |
| * In futex wake up scenarios where no tasks are blocked on a futex, taking |
| * the hb spinlock can be avoided and simply return. In order for this |
| * optimization to work, ordering guarantees must exist so that the waiter |
| * being added to the list is acknowledged when the list is concurrently being |
| * checked by the waker, avoiding scenarios like the following: |
| * |
| * CPU 0 CPU 1 |
| * val = *futex; |
| * sys_futex(WAIT, futex, val); |
| * futex_wait(futex, val); |
| * uval = *futex; |
| * *futex = newval; |
| * sys_futex(WAKE, futex); |
| * futex_wake(futex); |
| * if (queue_empty()) |
| * return; |
| * if (uval == val) |
| * lock(hash_bucket(futex)); |
| * queue(); |
| * unlock(hash_bucket(futex)); |
| * schedule(); |
| * |
| * This would cause the waiter on CPU 0 to wait forever because it |
| * missed the transition of the user space value from val to newval |
| * and the waker did not find the waiter in the hash bucket queue. |
| * |
| * The correct serialization ensures that a waiter either observes |
| * the changed user space value before blocking or is woken by a |
| * concurrent waker: |
| * |
| * CPU 0 CPU 1 |
| * val = *futex; |
| * sys_futex(WAIT, futex, val); |
| * futex_wait(futex, val); |
| * |
| * waiters++; (a) |
| * smp_mb(); (A) <-- paired with -. |
| * | |
| * lock(hash_bucket(futex)); | |
| * | |
| * uval = *futex; | |
| * | *futex = newval; |
| * | sys_futex(WAKE, futex); |
| * | futex_wake(futex); |
| * | |
| * `--------> smp_mb(); (B) |
| * if (uval == val) |
| * queue(); |
| * unlock(hash_bucket(futex)); |
| * schedule(); if (waiters) |
| * lock(hash_bucket(futex)); |
| * else wake_waiters(futex); |
| * waiters--; (b) unlock(hash_bucket(futex)); |
| * |
| * Where (A) orders the waiters increment and the futex value read through |
| * atomic operations (see hb_waiters_inc) and where (B) orders the write |
| * to futex and the waiters read -- this is done by the barriers for both |
| * shared and private futexes in get_futex_key_refs(). |
| * |
| * This yields the following case (where X:=waiters, Y:=futex): |
| * |
| * X = Y = 0 |
| * |
| * w[X]=1 w[Y]=1 |
| * MB MB |
| * r[Y]=y r[X]=x |
| * |
| * Which guarantees that x==0 && y==0 is impossible; which translates back into |
| * the guarantee that we cannot both miss the futex variable change and the |
| * enqueue. |
| * |
| * Note that a new waiter is accounted for in (a) even when it is possible that |
| * the wait call can return error, in which case we backtrack from it in (b). |
| * Refer to the comment in queue_lock(). |
| * |
| * Similarly, in order to account for waiters being requeued on another |
| * address we always increment the waiters for the destination bucket before |
| * acquiring the lock. It then decrements them again after releasing it - |
| * the code that actually moves the futex(es) between hash buckets (requeue_futex) |
| * will do the additional required waiter count housekeeping. This is done for |
| * double_lock_hb() and double_unlock_hb(), respectively. |
| */ |
| |
| #ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
| int __read_mostly futex_cmpxchg_enabled; |
| #endif |
| |
| /* |
| * Futex flags used to encode options to functions and preserve them across |
| * restarts. |
| */ |
| #ifdef CONFIG_MMU |
| # define FLAGS_SHARED 0x01 |
| #else |
| /* |
| * NOMMU does not have per process address space. Let the compiler optimize |
| * code away. |
| */ |
| # define FLAGS_SHARED 0x00 |
| #endif |
| #define FLAGS_CLOCKRT 0x02 |
| #define FLAGS_HAS_TIMEOUT 0x04 |
| |
| /* |
| * Priority Inheritance state: |
| */ |
| struct futex_pi_state { |
| /* |
| * list of 'owned' pi_state instances - these have to be |
| * cleaned up in do_exit() if the task exits prematurely: |
| */ |
| struct list_head list; |
| |
| /* |
| * The PI object: |
| */ |
| struct rt_mutex pi_mutex; |
| |
| struct task_struct *owner; |
| atomic_t refcount; |
| |
| union futex_key key; |
| }; |
| |
| /** |
| * struct futex_q - The hashed futex queue entry, one per waiting task |
| * @list: priority-sorted list of tasks waiting on this futex |
| * @task: the task waiting on the futex |
| * @lock_ptr: the hash bucket lock |
| * @key: the key the futex is hashed on |
| * @pi_state: optional priority inheritance state |
| * @rt_waiter: rt_waiter storage for use with requeue_pi |
| * @requeue_pi_key: the requeue_pi target futex key |
| * @bitset: bitset for the optional bitmasked wakeup |
| * |
| * We use this hashed waitqueue, instead of a normal wait_queue_t, so |
| * we can wake only the relevant ones (hashed queues may be shared). |
| * |
| * A futex_q has a woken state, just like tasks have TASK_RUNNING. |
| * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. |
| * The order of wakeup is always to make the first condition true, then |
| * the second. |
| * |
| * PI futexes are typically woken before they are removed from the hash list via |
| * the rt_mutex code. See unqueue_me_pi(). |
| */ |
| struct futex_q { |
| struct plist_node list; |
| |
| struct task_struct *task; |
| spinlock_t *lock_ptr; |
| union futex_key key; |
| struct futex_pi_state *pi_state; |
| struct rt_mutex_waiter *rt_waiter; |
| union futex_key *requeue_pi_key; |
| u32 bitset; |
| }; |
| |
| static const struct futex_q futex_q_init = { |
| /* list gets initialized in queue_me()*/ |
| .key = FUTEX_KEY_INIT, |
| .bitset = FUTEX_BITSET_MATCH_ANY |
| }; |
| |
| /* |
| * Hash buckets are shared by all the futex_keys that hash to the same |
| * location. Each key may have multiple futex_q structures, one for each task |
| * waiting on a futex. |
| */ |
| struct futex_hash_bucket { |
| atomic_t waiters; |
| spinlock_t lock; |
| struct plist_head chain; |
| } ____cacheline_aligned_in_smp; |
| |
| /* |
| * The base of the bucket array and its size are always used together |
| * (after initialization only in hash_futex()), so ensure that they |
| * reside in the same cacheline. |
| */ |
| static struct { |
| struct futex_hash_bucket *queues; |
| unsigned long hashsize; |
| } __futex_data __read_mostly __aligned(2*sizeof(long)); |
| #define futex_queues (__futex_data.queues) |
| #define futex_hashsize (__futex_data.hashsize) |
| |
| |
| /* |
| * Fault injections for futexes. |
| */ |
| #ifdef CONFIG_FAIL_FUTEX |
| |
| static struct { |
| struct fault_attr attr; |
| |
| bool ignore_private; |
| } fail_futex = { |
| .attr = FAULT_ATTR_INITIALIZER, |
| .ignore_private = false, |
| }; |
| |
| static int __init setup_fail_futex(char *str) |
| { |
| return setup_fault_attr(&fail_futex.attr, str); |
| } |
| __setup("fail_futex=", setup_fail_futex); |
| |
| static bool should_fail_futex(bool fshared) |
| { |
| if (fail_futex.ignore_private && !fshared) |
| return false; |
| |
| return should_fail(&fail_futex.attr, 1); |
| } |
| |
| #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS |
| |
| static int __init fail_futex_debugfs(void) |
| { |
| umode_t mode = S_IFREG | S_IRUSR | S_IWUSR; |
| struct dentry *dir; |
| |
| dir = fault_create_debugfs_attr("fail_futex", NULL, |
| &fail_futex.attr); |
| if (IS_ERR(dir)) |
| return PTR_ERR(dir); |
| |
| if (!debugfs_create_bool("ignore-private", mode, dir, |
| &fail_futex.ignore_private)) { |
| debugfs_remove_recursive(dir); |
| return -ENOMEM; |
| } |
| |
| return 0; |
| } |
| |
| late_initcall(fail_futex_debugfs); |
| |
| #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */ |
| |
| #else |
| static inline bool should_fail_futex(bool fshared) |
| { |
| return false; |
| } |
| #endif /* CONFIG_FAIL_FUTEX */ |
| |
| static inline void futex_get_mm(union futex_key *key) |
| { |
| atomic_inc(&key->private.mm->mm_count); |
| /* |
| * Ensure futex_get_mm() implies a full barrier such that |
| * get_futex_key() implies a full barrier. This is relied upon |
| * as smp_mb(); (B), see the ordering comment above. |
| */ |
| smp_mb__after_atomic(); |
| } |
| |
| /* |
| * Reflects a new waiter being added to the waitqueue. |
| */ |
| static inline void hb_waiters_inc(struct futex_hash_bucket *hb) |
| { |
| #ifdef CONFIG_SMP |
| atomic_inc(&hb->waiters); |
| /* |
| * Full barrier (A), see the ordering comment above. |
| */ |
| smp_mb__after_atomic(); |
| #endif |
| } |
| |
| /* |
| * Reflects a waiter being removed from the waitqueue by wakeup |
| * paths. |
| */ |
| static inline void hb_waiters_dec(struct futex_hash_bucket *hb) |
| { |
| #ifdef CONFIG_SMP |
| atomic_dec(&hb->waiters); |
| #endif |
| } |
| |
| static inline int hb_waiters_pending(struct futex_hash_bucket *hb) |
| { |
| #ifdef CONFIG_SMP |
| return atomic_read(&hb->waiters); |
| #else |
| return 1; |
| #endif |
| } |
| |
| /** |
| * hash_futex - Return the hash bucket in the global hash |
| * @key: Pointer to the futex key for which the hash is calculated |
| * |
| * We hash on the keys returned from get_futex_key (see below) and return the |
| * corresponding hash bucket in the global hash. |
| */ |
| static struct futex_hash_bucket *hash_futex(union futex_key *key) |
| { |
| u32 hash = jhash2((u32*)&key->both.word, |
| (sizeof(key->both.word)+sizeof(key->both.ptr))/4, |
| key->both.offset); |
| return &futex_queues[hash & (futex_hashsize - 1)]; |
| } |
| |
| |
| /** |
| * match_futex - Check whether two futex keys are equal |
| * @key1: Pointer to key1 |
| * @key2: Pointer to key2 |
| * |
| * Return 1 if two futex_keys are equal, 0 otherwise. |
| */ |
| static inline int match_futex(union futex_key *key1, union futex_key *key2) |
| { |
| return (key1 && key2 |
| && key1->both.word == key2->both.word |
| && key1->both.ptr == key2->both.ptr |
| && key1->both.offset == key2->both.offset); |
| } |
| |
| /* |
| * Take a reference to the resource addressed by a key. |
| * Can be called while holding spinlocks. |
| * |
| */ |
| static void get_futex_key_refs(union futex_key *key) |
| { |
| if (!key->both.ptr) |
| return; |
| |
| /* |
| * On MMU less systems futexes are always "private" as there is no per |
| * process address space. We need the smp wmb nevertheless - yes, |
| * arch/blackfin has MMU less SMP ... |
| */ |
| if (!IS_ENABLED(CONFIG_MMU)) { |
| smp_mb(); /* explicit smp_mb(); (B) */ |
| return; |
| } |
| |
| switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
| case FUT_OFF_INODE: |
| ihold(key->shared.inode); /* implies smp_mb(); (B) */ |
| break; |
| case FUT_OFF_MMSHARED: |
| futex_get_mm(key); /* implies smp_mb(); (B) */ |
| break; |
| default: |
| /* |
| * Private futexes do not hold reference on an inode or |
| * mm, therefore the only purpose of calling get_futex_key_refs |
| * is because we need the barrier for the lockless waiter check. |
| */ |
| smp_mb(); /* explicit smp_mb(); (B) */ |
| } |
| } |
| |
| /* |
| * Drop a reference to the resource addressed by a key. |
| * The hash bucket spinlock must not be held. This is |
| * a no-op for private futexes, see comment in the get |
| * counterpart. |
| */ |
| static void drop_futex_key_refs(union futex_key *key) |
| { |
| if (!key->both.ptr) { |
| /* If we're here then we tried to put a key we failed to get */ |
| WARN_ON_ONCE(1); |
| return; |
| } |
| |
| if (!IS_ENABLED(CONFIG_MMU)) |
| return; |
| |
| switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
| case FUT_OFF_INODE: |
| iput(key->shared.inode); |
| break; |
| case FUT_OFF_MMSHARED: |
| mmdrop(key->private.mm); |
| break; |
| } |
| } |
| |
| /** |
| * get_futex_key() - Get parameters which are the keys for a futex |
| * @uaddr: virtual address of the futex |
| * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED |
| * @key: address where result is stored. |
| * @rw: mapping needs to be read/write (values: VERIFY_READ, |
| * VERIFY_WRITE) |
| * |
| * Return: a negative error code or 0 |
| * |
| * The key words are stored in *key on success. |
| * |
| * For shared mappings, it's (page->index, file_inode(vma->vm_file), |
| * offset_within_page). For private mappings, it's (uaddr, current->mm). |
| * We can usually work out the index without swapping in the page. |
| * |
| * lock_page() might sleep, the caller should not hold a spinlock. |
| */ |
| static int |
| get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) |
| { |
| unsigned long address = (unsigned long)uaddr; |
| struct mm_struct *mm = current->mm; |
| struct page *page, *tail; |
| struct address_space *mapping; |
| int err, ro = 0; |
| |
| /* |
| * The futex address must be "naturally" aligned. |
| */ |
| key->both.offset = address % PAGE_SIZE; |
| if (unlikely((address % sizeof(u32)) != 0)) |
| return -EINVAL; |
| address -= key->both.offset; |
| |
| if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) |
| return -EFAULT; |
| |
| if (unlikely(should_fail_futex(fshared))) |
| return -EFAULT; |
| |
| /* |
| * PROCESS_PRIVATE futexes are fast. |
| * As the mm cannot disappear under us and the 'key' only needs |
| * virtual address, we dont even have to find the underlying vma. |
| * Note : We do have to check 'uaddr' is a valid user address, |
| * but access_ok() should be faster than find_vma() |
| */ |
| if (!fshared) { |
| key->private.mm = mm; |
| key->private.address = address; |
| get_futex_key_refs(key); /* implies smp_mb(); (B) */ |
| return 0; |
| } |
| |
| again: |
| /* Ignore any VERIFY_READ mapping (futex common case) */ |
| if (unlikely(should_fail_futex(fshared))) |
| return -EFAULT; |
| |
| err = get_user_pages_fast(address, 1, 1, &page); |
| /* |
| * If write access is not required (eg. FUTEX_WAIT), try |
| * and get read-only access. |
| */ |
| if (err == -EFAULT && rw == VERIFY_READ) { |
| err = get_user_pages_fast(address, 1, 0, &page); |
| ro = 1; |
| } |
| if (err < 0) |
| return err; |
| else |
| err = 0; |
| |
| /* |
| * The treatment of mapping from this point on is critical. The page |
| * lock protects many things but in this context the page lock |
| * stabilizes mapping, prevents inode freeing in the shared |
| * file-backed region case and guards against movement to swap cache. |
| * |
| * Strictly speaking the page lock is not needed in all cases being |
| * considered here and page lock forces unnecessarily serialization |
| * From this point on, mapping will be re-verified if necessary and |
| * page lock will be acquired only if it is unavoidable |
| * |
| * Mapping checks require the head page for any compound page so the |
| * head page and mapping is looked up now. For anonymous pages, it |
| * does not matter if the page splits in the future as the key is |
| * based on the address. For filesystem-backed pages, the tail is |
| * required as the index of the page determines the key. For |
| * base pages, there is no tail page and tail == page. |
| */ |
| tail = page; |
| page = compound_head(page); |
| mapping = READ_ONCE(page->mapping); |
| |
| /* |
| * If page->mapping is NULL, then it cannot be a PageAnon |
| * page; but it might be the ZERO_PAGE or in the gate area or |
| * in a special mapping (all cases which we are happy to fail); |
| * or it may have been a good file page when get_user_pages_fast |
| * found it, but truncated or holepunched or subjected to |
| * invalidate_complete_page2 before we got the page lock (also |
| * cases which we are happy to fail). And we hold a reference, |
| * so refcount care in invalidate_complete_page's remove_mapping |
| * prevents drop_caches from setting mapping to NULL beneath us. |
| * |
| * The case we do have to guard against is when memory pressure made |
| * shmem_writepage move it from filecache to swapcache beneath us: |
| * an unlikely race, but we do need to retry for page->mapping. |
| */ |
| if (unlikely(!mapping)) { |
| int shmem_swizzled; |
| |
| /* |
| * Page lock is required to identify which special case above |
| * applies. If this is really a shmem page then the page lock |
| * will prevent unexpected transitions. |
| */ |
| lock_page(page); |
| shmem_swizzled = PageSwapCache(page) || page->mapping; |
| unlock_page(page); |
| put_page(page); |
| |
| if (shmem_swizzled) |
| goto again; |
| |
| return -EFAULT; |
| } |
| |
| /* |
| * Private mappings are handled in a simple way. |
| * |
| * If the futex key is stored on an anonymous page, then the associated |
| * object is the mm which is implicitly pinned by the calling process. |
| * |
| * NOTE: When userspace waits on a MAP_SHARED mapping, even if |
| * it's a read-only handle, it's expected that futexes attach to |
| * the object not the particular process. |
| */ |
| if (PageAnon(page)) { |
| /* |
| * A RO anonymous page will never change and thus doesn't make |
| * sense for futex operations. |
| */ |
| if (unlikely(should_fail_futex(fshared)) || ro) { |
| err = -EFAULT; |
| goto out; |
| } |
| |
| key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ |
| key->private.mm = mm; |
| key->private.address = address; |
| |
| get_futex_key_refs(key); /* implies smp_mb(); (B) */ |
| |
| } else { |
| struct inode *inode; |
| |
| /* |
| * The associated futex object in this case is the inode and |
| * the page->mapping must be traversed. Ordinarily this should |
| * be stabilised under page lock but it's not strictly |
| * necessary in this case as we just want to pin the inode, not |
| * update the radix tree or anything like that. |
| * |
| * The RCU read lock is taken as the inode is finally freed |
| * under RCU. If the mapping still matches expectations then the |
| * mapping->host can be safely accessed as being a valid inode. |
| */ |
| rcu_read_lock(); |
| |
| if (READ_ONCE(page->mapping) != mapping) { |
| rcu_read_unlock(); |
| put_page(page); |
| |
| goto again; |
| } |
| |
| inode = READ_ONCE(mapping->host); |
| if (!inode) { |
| rcu_read_unlock(); |
| put_page(page); |
| |
| goto again; |
| } |
| |
| /* |
| * Take a reference unless it is about to be freed. Previously |
| * this reference was taken by ihold under the page lock |
| * pinning the inode in place so i_lock was unnecessary. The |
| * only way for this check to fail is if the inode was |
| * truncated in parallel so warn for now if this happens. |
| * |
| * We are not calling into get_futex_key_refs() in file-backed |
| * cases, therefore a successful atomic_inc return below will |
| * guarantee that get_futex_key() will still imply smp_mb(); (B). |
| */ |
| if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) { |
| rcu_read_unlock(); |
| put_page(page); |
| |
| goto again; |
| } |
| |
| /* Should be impossible but lets be paranoid for now */ |
| if (WARN_ON_ONCE(inode->i_mapping != mapping)) { |
| err = -EFAULT; |
| rcu_read_unlock(); |
| iput(inode); |
| |
| goto out; |
| } |
| |
| key->both.offset |= FUT_OFF_INODE; /* inode-based key */ |
| key->shared.inode = inode; |
| key->shared.pgoff = basepage_index(tail); |
| rcu_read_unlock(); |
| } |
| |
| out: |
| put_page(page); |
| return err; |
| } |
| |
| static inline void put_futex_key(union futex_key *key) |
| { |
| drop_futex_key_refs(key); |
| } |
| |
| /** |
| * fault_in_user_writeable() - Fault in user address and verify RW access |
| * @uaddr: pointer to faulting user space address |
| * |
| * Slow path to fixup the fault we just took in the atomic write |
| * access to @uaddr. |
| * |
| * We have no generic implementation of a non-destructive write to the |
| * user address. We know that we faulted in the atomic pagefault |
| * disabled section so we can as well avoid the #PF overhead by |
| * calling get_user_pages() right away. |
| */ |
| static int fault_in_user_writeable(u32 __user *uaddr) |
| { |
| struct mm_struct *mm = current->mm; |
| int ret; |
| |
| down_read(&mm->mmap_sem); |
| ret = fixup_user_fault(current, mm, (unsigned long)uaddr, |
| FAULT_FLAG_WRITE, NULL); |
| up_read(&mm->mmap_sem); |
| |
| return ret < 0 ? ret : 0; |
| } |
| |
| /** |
| * futex_top_waiter() - Return the highest priority waiter on a futex |
| * @hb: the hash bucket the futex_q's reside in |
| * @key: the futex key (to distinguish it from other futex futex_q's) |
| * |
| * Must be called with the hb lock held. |
| */ |
| static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, |
| union futex_key *key) |
| { |
| struct futex_q *this; |
| |
| plist_for_each_entry(this, &hb->chain, list) { |
| if (match_futex(&this->key, key)) |
| return this; |
| } |
| return NULL; |
| } |
| |
| static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, |
| u32 uval, u32 newval) |
| { |
| int ret; |
| |
| pagefault_disable(); |
| ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); |
| pagefault_enable(); |
| |
| return ret; |
| } |
| |
| static int get_futex_value_locked(u32 *dest, u32 __user *from) |
| { |
| int ret; |
| |
| pagefault_disable(); |
| ret = __get_user(*dest, from); |
| pagefault_enable(); |
| |
| return ret ? -EFAULT : 0; |
| } |
| |
| |
| /* |
| * PI code: |
| */ |
| static int refill_pi_state_cache(void) |
| { |
| struct futex_pi_state *pi_state; |
| |
| if (likely(current->pi_state_cache)) |
| return 0; |
| |
| pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); |
| |
| if (!pi_state) |
| return -ENOMEM; |
| |
| INIT_LIST_HEAD(&pi_state->list); |
| /* pi_mutex gets initialized later */ |
| pi_state->owner = NULL; |
| atomic_set(&pi_state->refcount, 1); |
| pi_state->key = FUTEX_KEY_INIT; |
| |
| current->pi_state_cache = pi_state; |
| |
| return 0; |
| } |
| |
| static struct futex_pi_state * alloc_pi_state(void) |
| { |
| struct futex_pi_state *pi_state = current->pi_state_cache; |
| |
| WARN_ON(!pi_state); |
| current->pi_state_cache = NULL; |
| |
| return pi_state; |
| } |
| |
| /* |
| * Drops a reference to the pi_state object and frees or caches it |
| * when the last reference is gone. |
| * |
| * Must be called with the hb lock held. |
| */ |
| static void put_pi_state(struct futex_pi_state *pi_state) |
| { |
| if (!pi_state) |
| return; |
| |
| if (!atomic_dec_and_test(&pi_state->refcount)) |
| return; |
| |
| /* |
| * If pi_state->owner is NULL, the owner is most probably dying |
| * and has cleaned up the pi_state already |
| */ |
| if (pi_state->owner) { |
| raw_spin_lock_irq(&pi_state->owner->pi_lock); |
| list_del_init(&pi_state->list); |
| raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
| |
| rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); |
| } |
| |
| if (current->pi_state_cache) |
| kfree(pi_state); |
| else { |
| /* |
| * pi_state->list is already empty. |
| * clear pi_state->owner. |
| * refcount is at 0 - put it back to 1. |
| */ |
| pi_state->owner = NULL; |
| atomic_set(&pi_state->refcount, 1); |
| current->pi_state_cache = pi_state; |
| } |
| } |
| |
| /* |
| * Look up the task based on what TID userspace gave us. |
| * We dont trust it. |
| */ |
| static struct task_struct * futex_find_get_task(pid_t pid) |
| { |
| struct task_struct *p; |
| |
| rcu_read_lock(); |
| p = find_task_by_vpid(pid); |
| if (p) |
| get_task_struct(p); |
| |
| rcu_read_unlock(); |
| |
| return p; |
| } |
| |
| /* |
| * This task is holding PI mutexes at exit time => bad. |
| * Kernel cleans up PI-state, but userspace is likely hosed. |
| * (Robust-futex cleanup is separate and might save the day for userspace.) |
| */ |
| void exit_pi_state_list(struct task_struct *curr) |
| { |
| struct list_head *next, *head = &curr->pi_state_list; |
| struct futex_pi_state *pi_state; |
| struct futex_hash_bucket *hb; |
| union futex_key key = FUTEX_KEY_INIT; |
| |
| if (!futex_cmpxchg_enabled) |
| return; |
| /* |
| * We are a ZOMBIE and nobody can enqueue itself on |
| * pi_state_list anymore, but we have to be careful |
| * versus waiters unqueueing themselves: |
| */ |
| raw_spin_lock_irq(&curr->pi_lock); |
| while (!list_empty(head)) { |
| |
| next = head->next; |
| pi_state = list_entry(next, struct futex_pi_state, list); |
| key = pi_state->key; |
| hb = hash_futex(&key); |
| raw_spin_unlock_irq(&curr->pi_lock); |
| |
| spin_lock(&hb->lock); |
| |
| raw_spin_lock_irq(&curr->pi_lock); |
| /* |
| * We dropped the pi-lock, so re-check whether this |
| * task still owns the PI-state: |
| */ |
| if (head->next != next) { |
| spin_unlock(&hb->lock); |
| continue; |
| } |
| |
| WARN_ON(pi_state->owner != curr); |
| WARN_ON(list_empty(&pi_state->list)); |
| list_del_init(&pi_state->list); |
| pi_state->owner = NULL; |
| raw_spin_unlock_irq(&curr->pi_lock); |
| |
| rt_mutex_unlock(&pi_state->pi_mutex); |
| |
| spin_unlock(&hb->lock); |
| |
| raw_spin_lock_irq(&curr->pi_lock); |
| } |
| raw_spin_unlock_irq(&curr->pi_lock); |
| } |
| |
| /* |
| * We need to check the following states: |
| * |
| * Waiter | pi_state | pi->owner | uTID | uODIED | ? |
| * |
| * [1] NULL | --- | --- | 0 | 0/1 | Valid |
| * [2] NULL | --- | --- | >0 | 0/1 | Valid |
| * |
| * [3] Found | NULL | -- | Any | 0/1 | Invalid |
| * |
| * [4] Found | Found | NULL | 0 | 1 | Valid |
| * [5] Found | Found | NULL | >0 | 1 | Invalid |
| * |
| * [6] Found | Found | task | 0 | 1 | Valid |
| * |
| * [7] Found | Found | NULL | Any | 0 | Invalid |
| * |
| * [8] Found | Found | task | ==taskTID | 0/1 | Valid |
| * [9] Found | Found | task | 0 | 0 | Invalid |
| * [10] Found | Found | task | !=taskTID | 0/1 | Invalid |
| * |
| * [1] Indicates that the kernel can acquire the futex atomically. We |
| * came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit. |
| * |
| * [2] Valid, if TID does not belong to a kernel thread. If no matching |
| * thread is found then it indicates that the owner TID has died. |
| * |
| * [3] Invalid. The waiter is queued on a non PI futex |
| * |
| * [4] Valid state after exit_robust_list(), which sets the user space |
| * value to FUTEX_WAITERS | FUTEX_OWNER_DIED. |
| * |
| * [5] The user space value got manipulated between exit_robust_list() |
| * and exit_pi_state_list() |
| * |
| * [6] Valid state after exit_pi_state_list() which sets the new owner in |
| * the pi_state but cannot access the user space value. |
| * |
| * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set. |
| * |
| * [8] Owner and user space value match |
| * |
| * [9] There is no transient state which sets the user space TID to 0 |
| * except exit_robust_list(), but this is indicated by the |
| * FUTEX_OWNER_DIED bit. See [4] |
| * |
| * [10] There is no transient state which leaves owner and user space |
| * TID out of sync. |
| */ |
| |
| /* |
| * Validate that the existing waiter has a pi_state and sanity check |
| * the pi_state against the user space value. If correct, attach to |
| * it. |
| */ |
| static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state, |
| struct futex_pi_state **ps) |
| { |
| pid_t pid = uval & FUTEX_TID_MASK; |
| |
| /* |
| * Userspace might have messed up non-PI and PI futexes [3] |
| */ |
| if (unlikely(!pi_state)) |
| return -EINVAL; |
| |
| WARN_ON(!atomic_read(&pi_state->refcount)); |
| |
| /* |
| * Handle the owner died case: |
| */ |
| if (uval & FUTEX_OWNER_DIED) { |
| /* |
| * exit_pi_state_list sets owner to NULL and wakes the |
| * topmost waiter. The task which acquires the |
| * pi_state->rt_mutex will fixup owner. |
| */ |
| if (!pi_state->owner) { |
| /* |
| * No pi state owner, but the user space TID |
| * is not 0. Inconsistent state. [5] |
| */ |
| if (pid) |
| return -EINVAL; |
| /* |
| * Take a ref on the state and return success. [4] |
| */ |
| goto out_state; |
| } |
| |
| /* |
| * If TID is 0, then either the dying owner has not |
| * yet executed exit_pi_state_list() or some waiter |
| * acquired the rtmutex in the pi state, but did not |
| * yet fixup the TID in user space. |
| * |
| * Take a ref on the state and return success. [6] |
| */ |
| if (!pid) |
| goto out_state; |
| } else { |
| /* |
| * If the owner died bit is not set, then the pi_state |
| * must have an owner. [7] |
| */ |
| if (!pi_state->owner) |
| return -EINVAL; |
| } |
| |
| /* |
| * Bail out if user space manipulated the futex value. If pi |
| * state exists then the owner TID must be the same as the |
| * user space TID. [9/10] |
| */ |
| if (pid != task_pid_vnr(pi_state->owner)) |
| return -EINVAL; |
| out_state: |
| atomic_inc(&pi_state->refcount); |
| *ps = pi_state; |
| return 0; |
| } |
| |
| /* |
| * Lookup the task for the TID provided from user space and attach to |
| * it after doing proper sanity checks. |
| */ |
| static int attach_to_pi_owner(u32 uval, union futex_key *key, |
| struct futex_pi_state **ps) |
| { |
| pid_t pid = uval & FUTEX_TID_MASK; |
| struct futex_pi_state *pi_state; |
| struct task_struct *p; |
| |
| /* |
| * We are the first waiter - try to look up the real owner and attach |
| * the new pi_state to it, but bail out when TID = 0 [1] |
| */ |
| if (!pid) |
| return -ESRCH; |
| p = futex_find_get_task(pid); |
| if (!p) |
| return -ESRCH; |
| |
| if (unlikely(p->flags & PF_KTHREAD)) { |
| put_task_struct(p); |
| return -EPERM; |
| } |
| |
| /* |
| * We need to look at the task state flags to figure out, |
| * whether the task is exiting. To protect against the do_exit |
| * change of the task flags, we do this protected by |
| * p->pi_lock: |
| */ |
| raw_spin_lock_irq(&p->pi_lock); |
| if (unlikely(p->flags & PF_EXITING)) { |
| /* |
| * The task is on the way out. When PF_EXITPIDONE is |
| * set, we know that the task has finished the |
| * cleanup: |
| */ |
| int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; |
| |
| raw_spin_unlock_irq(&p->pi_lock); |
| put_task_struct(p); |
| return ret; |
| } |
| |
| /* |
| * No existing pi state. First waiter. [2] |
| */ |
| pi_state = alloc_pi_state(); |
| |
| /* |
| * Initialize the pi_mutex in locked state and make @p |
| * the owner of it: |
| */ |
| rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); |
| |
| /* Store the key for possible exit cleanups: */ |
| pi_state->key = *key; |
| |
| WARN_ON(!list_empty(&pi_state->list)); |
| list_add(&pi_state->list, &p->pi_state_list); |
| pi_state->owner = p; |
| raw_spin_unlock_irq(&p->pi_lock); |
| |
| put_task_struct(p); |
| |
| *ps = pi_state; |
| |
| return 0; |
| } |
| |
| static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, |
| union futex_key *key, struct futex_pi_state **ps) |
| { |
| struct futex_q *match = futex_top_waiter(hb, key); |
| |
| /* |
| * If there is a waiter on that futex, validate it and |
| * attach to the pi_state when the validation succeeds. |
| */ |
| if (match) |
| return attach_to_pi_state(uval, match->pi_state, ps); |
| |
| /* |
| * We are the first waiter - try to look up the owner based on |
| * @uval and attach to it. |
| */ |
| return attach_to_pi_owner(uval, key, ps); |
| } |
| |
| static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) |
| { |
| u32 uninitialized_var(curval); |
| |
| if (unlikely(should_fail_futex(true))) |
| return -EFAULT; |
| |
| if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) |
| return -EFAULT; |
| |
| /*If user space value changed, let the caller retry */ |
| return curval != uval ? -EAGAIN : 0; |
| } |
| |
| /** |
| * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex |
| * @uaddr: the pi futex user address |
| * @hb: the pi futex hash bucket |
| * @key: the futex key associated with uaddr and hb |
| * @ps: the pi_state pointer where we store the result of the |
| * lookup |
| * @task: the task to perform the atomic lock work for. This will |
| * be "current" except in the case of requeue pi. |
| * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
| * |
| * Return: |
| * 0 - ready to wait; |
| * 1 - acquired the lock; |
| * <0 - error |
| * |
| * The hb->lock and futex_key refs shall be held by the caller. |
| */ |
| static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, |
| union futex_key *key, |
| struct futex_pi_state **ps, |
| struct task_struct *task, int set_waiters) |
| { |
| u32 uval, newval, vpid = task_pid_vnr(task); |
| struct futex_q *match; |
| int ret; |
| |
| /* |
| * Read the user space value first so we can validate a few |
| * things before proceeding further. |
| */ |
| if (get_futex_value_locked(&uval, uaddr)) |
| return -EFAULT; |
| |
| if (unlikely(should_fail_futex(true))) |
| return -EFAULT; |
| |
| /* |
| * Detect deadlocks. |
| */ |
| if ((unlikely((uval & FUTEX_TID_MASK) == vpid))) |
| return -EDEADLK; |
| |
| if ((unlikely(should_fail_futex(true)))) |
| return -EDEADLK; |
| |
| /* |
| * Lookup existing state first. If it exists, try to attach to |
| * its pi_state. |
| */ |
| match = futex_top_waiter(hb, key); |
| if (match) |
| return attach_to_pi_state(uval, match->pi_state, ps); |
| |
| /* |
| * No waiter and user TID is 0. We are here because the |
| * waiters or the owner died bit is set or called from |
| * requeue_cmp_pi or for whatever reason something took the |
| * syscall. |
| */ |
| if (!(uval & FUTEX_TID_MASK)) { |
| /* |
| * We take over the futex. No other waiters and the user space |
| * TID is 0. We preserve the owner died bit. |
| */ |
| newval = uval & FUTEX_OWNER_DIED; |
| newval |= vpid; |
| |
| /* The futex requeue_pi code can enforce the waiters bit */ |
| if (set_waiters) |
| newval |= FUTEX_WAITERS; |
| |
| ret = lock_pi_update_atomic(uaddr, uval, newval); |
| /* If the take over worked, return 1 */ |
| return ret < 0 ? ret : 1; |
| } |
| |
| /* |
| * First waiter. Set the waiters bit before attaching ourself to |
| * the owner. If owner tries to unlock, it will be forced into |
| * the kernel and blocked on hb->lock. |
| */ |
| newval = uval | FUTEX_WAITERS; |
| ret = lock_pi_update_atomic(uaddr, uval, newval); |
| if (ret) |
| return ret; |
| /* |
| * If the update of the user space value succeeded, we try to |
| * attach to the owner. If that fails, no harm done, we only |
| * set the FUTEX_WAITERS bit in the user space variable. |
| */ |
| return attach_to_pi_owner(uval, key, ps); |
| } |
| |
| /** |
| * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket |
| * @q: The futex_q to unqueue |
| * |
| * The q->lock_ptr must not be NULL and must be held by the caller. |
| */ |
| static void __unqueue_futex(struct futex_q *q) |
| { |
| struct futex_hash_bucket *hb; |
| |
| if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) |
| || WARN_ON(plist_node_empty(&q->list))) |
| return; |
| |
| hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); |
| plist_del(&q->list, &hb->chain); |
| hb_waiters_dec(hb); |
| } |
| |
| /* |
| * The hash bucket lock must be held when this is called. |
| * Afterwards, the futex_q must not be accessed. Callers |
| * must ensure to later call wake_up_q() for the actual |
| * wakeups to occur. |
| */ |
| static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q) |
| { |
| struct task_struct *p = q->task; |
| |
| if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n")) |
| return; |
| |
| /* |
| * Queue the task for later wakeup for after we've released |
| * the hb->lock. wake_q_add() grabs reference to p. |
| */ |
| wake_q_add(wake_q, p); |
| __unqueue_futex(q); |
| /* |
| * The waiting task can free the futex_q as soon as |
| * q->lock_ptr = NULL is written, without taking any locks. A |
| * memory barrier is required here to prevent the following |
| * store to lock_ptr from getting ahead of the plist_del. |
| */ |
| smp_wmb(); |
| q->lock_ptr = NULL; |
| } |
| |
| static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this, |
| struct futex_hash_bucket *hb) |
| { |
| struct task_struct *new_owner; |
| struct futex_pi_state *pi_state = this->pi_state; |
| u32 uninitialized_var(curval), newval; |
| DEFINE_WAKE_Q(wake_q); |
| bool deboost; |
| int ret = 0; |
| |
| if (!pi_state) |
| return -EINVAL; |
| |
| /* |
| * If current does not own the pi_state then the futex is |
| * inconsistent and user space fiddled with the futex value. |
| */ |
| if (pi_state->owner != current) |
| return -EINVAL; |
| |
| raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); |
| new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); |
| |
| /* |
| * It is possible that the next waiter (the one that brought |
| * this owner to the kernel) timed out and is no longer |
| * waiting on the lock. |
| */ |
| if (!new_owner) |
| new_owner = this->task; |
| |
| /* |
| * We pass it to the next owner. The WAITERS bit is always |
| * kept enabled while there is PI state around. We cleanup the |
| * owner died bit, because we are the owner. |
| */ |
| newval = FUTEX_WAITERS | task_pid_vnr(new_owner); |
| |
| if (unlikely(should_fail_futex(true))) |
| ret = -EFAULT; |
| |
| if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) { |
| ret = -EFAULT; |
| } else if (curval != uval) { |
| /* |
| * If a unconditional UNLOCK_PI operation (user space did not |
| * try the TID->0 transition) raced with a waiter setting the |
| * FUTEX_WAITERS flag between get_user() and locking the hash |
| * bucket lock, retry the operation. |
| */ |
| if ((FUTEX_TID_MASK & curval) == uval) |
| ret = -EAGAIN; |
| else |
| ret = -EINVAL; |
| } |
| if (ret) { |
| raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
| return ret; |
| } |
| |
| raw_spin_lock(&pi_state->owner->pi_lock); |
| WARN_ON(list_empty(&pi_state->list)); |
| list_del_init(&pi_state->list); |
| raw_spin_unlock(&pi_state->owner->pi_lock); |
| |
| raw_spin_lock(&new_owner->pi_lock); |
| WARN_ON(!list_empty(&pi_state->list)); |
| list_add(&pi_state->list, &new_owner->pi_state_list); |
| pi_state->owner = new_owner; |
| raw_spin_unlock(&new_owner->pi_lock); |
| |
| raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); |
| |
| deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q); |
| |
| /* |
| * First unlock HB so the waiter does not spin on it once he got woken |
| * up. Second wake up the waiter before the priority is adjusted. If we |
| * deboost first (and lose our higher priority), then the task might get |
| * scheduled away before the wake up can take place. |
| */ |
| spin_unlock(&hb->lock); |
| wake_up_q(&wake_q); |
| if (deboost) |
| rt_mutex_adjust_prio(current); |
| |
| return 0; |
| } |
| |
| /* |
| * Express the locking dependencies for lockdep: |
| */ |
| static inline void |
| double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
| { |
| if (hb1 <= hb2) { |
| spin_lock(&hb1->lock); |
| if (hb1 < hb2) |
| spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); |
| } else { /* hb1 > hb2 */ |
| spin_lock(&hb2->lock); |
| spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); |
| } |
| } |
| |
| static inline void |
| double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
| { |
| spin_unlock(&hb1->lock); |
| if (hb1 != hb2) |
| spin_unlock(&hb2->lock); |
| } |
| |
| /* |
| * Wake up waiters matching bitset queued on this futex (uaddr). |
| */ |
| static int |
| futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) |
| { |
| struct futex_hash_bucket *hb; |
| struct futex_q *this, *next; |
| union futex_key key = FUTEX_KEY_INIT; |
| int ret; |
| DEFINE_WAKE_Q(wake_q); |
| |
| if (!bitset) |
| return -EINVAL; |
| |
| ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ); |
| if (unlikely(ret != 0)) |
| goto out; |
| |
| hb = hash_futex(&key); |
| |
| /* Make sure we really have tasks to wakeup */ |
| if (!hb_waiters_pending(hb)) |
| goto out_put_key; |
| |
| spin_lock(&hb->lock); |
| |
| plist_for_each_entry_safe(this, next, &hb->chain, list) { |
| if (match_futex (&this->key, &key)) { |
| if (this->pi_state || this->rt_waiter) { |
| ret = -EINVAL; |
| break; |
| } |
| |
| /* Check if one of the bits is set in both bitsets */ |
| if (!(this->bitset & bitset)) |
| continue; |
| |
| mark_wake_futex(&wake_q, this); |
| if (++ret >= nr_wake) |
| break; |
| } |
| } |
| |
| spin_unlock(&hb->lock); |
| wake_up_q(&wake_q); |
| out_put_key: |
| put_futex_key(&key); |
| out: |
| return ret; |
| } |
| |
| /* |
| * Wake up all waiters hashed on the physical page that is mapped |
| * to this virtual address: |
| */ |
| static int |
| futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, |
| int nr_wake, int nr_wake2, int op) |
| { |
| union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
| struct futex_hash_bucket *hb1, *hb2; |
| struct futex_q *this, *next; |
| int ret, op_ret; |
| DEFINE_WAKE_Q(wake_q); |
| |
| retry: |
| ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
| if (unlikely(ret != 0)) |
| goto out; |
| ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
| if (unlikely(ret != 0)) |
| goto out_put_key1; |
| |
| hb1 = hash_futex(&key1); |
| hb2 = hash_futex(&key2); |
| |
| retry_private: |
| double_lock_hb(hb1, hb2); |
| op_ret = futex_atomic_op_inuser(op, uaddr2); |
| if (unlikely(op_ret < 0)) { |
| |
| double_unlock_hb(hb1, hb2); |
| |
| #ifndef CONFIG_MMU |
| /* |
| * we don't get EFAULT from MMU faults if we don't have an MMU, |
| * but we might get them from range checking |
| */ |
| ret = op_ret; |
| goto out_put_keys; |
| #endif |
| |
| if (unlikely(op_ret != -EFAULT)) { |
| ret = op_ret; |
| goto out_put_keys; |
| } |
| |
| ret = fault_in_user_writeable(uaddr2); |
| if (ret) |
| goto out_put_keys; |
| |
| if (!(flags & FLAGS_SHARED)) |
| goto retry_private; |
| |
| put_futex_key(&key2); |
| put_futex_key(&key1); |
| goto retry; |
| } |
| |
| plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
| if (match_futex (&this->key, &key1)) { |
| if (this->pi_state || this->rt_waiter) { |
| ret = -EINVAL; |
| goto out_unlock; |
| } |
| mark_wake_futex(&wake_q, this); |
| if (++ret >= nr_wake) |
| break; |
| } |
| } |
| |
| if (op_ret > 0) { |
| op_ret = 0; |
| plist_for_each_entry_safe(this, next, &hb2->chain, list) { |
| if (match_futex (&this->key, &key2)) { |
| if (this->pi_state || this->rt_waiter) { |
| ret = -EINVAL; |
| goto out_unlock; |
| } |
| mark_wake_futex(&wake_q, this); |
| if (++op_ret >= nr_wake2) |
| break; |
| } |
| } |
| ret += op_ret; |
| } |
| |
| out_unlock: |
| double_unlock_hb(hb1, hb2); |
| wake_up_q(&wake_q); |
| out_put_keys: |
| put_futex_key(&key2); |
| out_put_key1: |
| put_futex_key(&key1); |
| out: |
| return ret; |
| } |
| |
| /** |
| * requeue_futex() - Requeue a futex_q from one hb to another |
| * @q: the futex_q to requeue |
| * @hb1: the source hash_bucket |
| * @hb2: the target hash_bucket |
| * @key2: the new key for the requeued futex_q |
| */ |
| static inline |
| void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, |
| struct futex_hash_bucket *hb2, union futex_key *key2) |
| { |
| |
| /* |
| * If key1 and key2 hash to the same bucket, no need to |
| * requeue. |
| */ |
| if (likely(&hb1->chain != &hb2->chain)) { |
| plist_del(&q->list, &hb1->chain); |
| hb_waiters_dec(hb1); |
| hb_waiters_inc(hb2); |
| plist_add(&q->list, &hb2->chain); |
| q->lock_ptr = &hb2->lock; |
| } |
| get_futex_key_refs(key2); |
| q->key = *key2; |
| } |
| |
| /** |
| * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue |
| * @q: the futex_q |
| * @key: the key of the requeue target futex |
| * @hb: the hash_bucket of the requeue target futex |
| * |
| * During futex_requeue, with requeue_pi=1, it is possible to acquire the |
| * target futex if it is uncontended or via a lock steal. Set the futex_q key |
| * to the requeue target futex so the waiter can detect the wakeup on the right |
| * futex, but remove it from the hb and NULL the rt_waiter so it can detect |
| * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock |
| * to protect access to the pi_state to fixup the owner later. Must be called |
| * with both q->lock_ptr and hb->lock held. |
| */ |
| static inline |
| void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |
| struct futex_hash_bucket *hb) |
| { |
| get_futex_key_refs(key); |
| q->key = *key; |
| |
| __unqueue_futex(q); |
| |
| WARN_ON(!q->rt_waiter); |
| q->rt_waiter = NULL; |
| |
| q->lock_ptr = &hb->lock; |
| |
| wake_up_state(q->task, TASK_NORMAL); |
| } |
| |
| /** |
| * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter |
| * @pifutex: the user address of the to futex |
| * @hb1: the from futex hash bucket, must be locked by the caller |
| * @hb2: the to futex hash bucket, must be locked by the caller |
| * @key1: the from futex key |
| * @key2: the to futex key |
| * @ps: address to store the pi_state pointer |
| * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
| * |
| * Try and get the lock on behalf of the top waiter if we can do it atomically. |
| * Wake the top waiter if we succeed. If the caller specified set_waiters, |
| * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. |
| * hb1 and hb2 must be held by the caller. |
| * |
| * Return: |
| * 0 - failed to acquire the lock atomically; |
| * >0 - acquired the lock, return value is vpid of the top_waiter |
| * <0 - error |
| */ |
| static int futex_proxy_trylock_atomic(u32 __user *pifutex, |
| struct futex_hash_bucket *hb1, |
| struct futex_hash_bucket *hb2, |
| union futex_key *key1, union futex_key *key2, |
| struct futex_pi_state **ps, int set_waiters) |
| { |
| struct futex_q *top_waiter = NULL; |
| u32 curval; |
| int ret, vpid; |
| |
| if (get_futex_value_locked(&curval, pifutex)) |
| return -EFAULT; |
| |
| if (unlikely(should_fail_futex(true))) |
| return -EFAULT; |
| |
| /* |
| * Find the top_waiter and determine if there are additional waiters. |
| * If the caller intends to requeue more than 1 waiter to pifutex, |
| * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, |
| * as we have means to handle the possible fault. If not, don't set |
| * the bit unecessarily as it will force the subsequent unlock to enter |
| * the kernel. |
| */ |
| top_waiter = futex_top_waiter(hb1, key1); |
| |
| /* There are no waiters, nothing for us to do. */ |
| if (!top_waiter) |
| return 0; |
| |
| /* Ensure we requeue to the expected futex. */ |
| if (!match_futex(top_waiter->requeue_pi_key, key2)) |
| return -EINVAL; |
| |
| /* |
| * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in |
| * the contended case or if set_waiters is 1. The pi_state is returned |
| * in ps in contended cases. |
| */ |
| vpid = task_pid_vnr(top_waiter->task); |
| ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, |
| set_waiters); |
| if (ret == 1) { |
| requeue_pi_wake_futex(top_waiter, key2, hb2); |
| return vpid; |
| } |
| return ret; |
| } |
| |
| /** |
| * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 |
| * @uaddr1: source futex user address |
| * @flags: futex flags (FLAGS_SHARED, etc.) |
| * @uaddr2: target futex user address |
| * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) |
| * @nr_requeue: number of waiters to requeue (0-INT_MAX) |
| * @cmpval: @uaddr1 expected value (or %NULL) |
| * @requeue_pi: if we are attempting to requeue from a non-pi futex to a |
| * pi futex (pi to pi requeue is not supported) |
| * |
| * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire |
| * uaddr2 atomically on behalf of the top waiter. |
| * |
| * Return: |
| * >=0 - on success, the number of tasks requeued or woken; |
| * <0 - on error |
| */ |
| static int futex_requeue(u32 __user *uaddr1, unsigned int flags, |
| u32 __user *uaddr2, int nr_wake, int nr_requeue, |
| u32 *cmpval, int requeue_pi) |
| { |
| union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
| int drop_count = 0, task_count = 0, ret; |
| struct futex_pi_state *pi_state = NULL; |
| struct futex_hash_bucket *hb1, *hb2; |
| struct futex_q *this, *next; |
| DEFINE_WAKE_Q(wake_q); |
| |
| if (requeue_pi) { |
| /* |
| * Requeue PI only works on two distinct uaddrs. This |
| * check is only valid for private futexes. See below. |
| */ |
| if (uaddr1 == uaddr2) |
| return -EINVAL; |
| |
| /* |
| * requeue_pi requires a pi_state, try to allocate it now |
| * without any locks in case it fails. |
| */ |
| if (refill_pi_state_cache()) |
| return -ENOMEM; |
| /* |
| * requeue_pi must wake as many tasks as it can, up to nr_wake |
| * + nr_requeue, since it acquires the rt_mutex prior to |
| * returning to userspace, so as to not leave the rt_mutex with |
| * waiters and no owner. However, second and third wake-ups |
| * cannot be predicted as they involve race conditions with the |
| * first wake and a fault while looking up the pi_state. Both |
| * pthread_cond_signal() and pthread_cond_broadcast() should |
| * use nr_wake=1. |
| */ |
| if (nr_wake != 1) |
| return -EINVAL; |
| } |
| |
| retry: |
| ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
| if (unlikely(ret != 0)) |
| goto out; |
| ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, |
| requeue_pi ? VERIFY_WRITE : VERIFY_READ); |
| if (unlikely(ret != 0)) |
| goto out_put_key1; |
| |
| /* |
| * The check above which compares uaddrs is not sufficient for |
| * shared futexes. We need to compare the keys: |
| */ |
| if (requeue_pi && match_futex(&key1, &key2)) { |
| ret = -EINVAL; |
| goto out_put_keys; |
| } |
| |
| hb1 = hash_futex(&key1); |
| hb2 = hash_futex(&key2); |
| |
| retry_private: |
| hb_waiters_inc(hb2); |
| double_lock_hb(hb1, hb2); |
| |
| if (likely(cmpval != NULL)) { |
| u32 curval; |
| |
| ret = get_futex_value_locked(&curval, uaddr1); |
| |
| if (unlikely(ret)) { |
| double_unlock_hb(hb1, hb2); |
| hb_waiters_dec(hb2); |
| |
| ret = get_user(curval, uaddr1); |
| if (ret) |
| goto out_put_keys; |
| |
| if (!(flags & FLAGS_SHARED)) |
| goto retry_private; |
| |
| put_futex_key(&key2); |
| put_futex_key(&key1); |
| goto retry; |
| } |
| if (curval != *cmpval) { |
| ret = -EAGAIN; |
| goto out_unlock; |
| } |
| } |
| |
| if (requeue_pi && (task_count - nr_wake < nr_requeue)) { |
| /* |
| * Attempt to acquire uaddr2 and wake the top waiter. If we |
| * intend to requeue waiters, force setting the FUTEX_WAITERS |
| * bit. We force this here where we are able to easily handle |
| * faults rather in the requeue loop below. |
| */ |
| ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, |
| &key2, &pi_state, nr_requeue); |
| |
| /* |
| * At this point the top_waiter has either taken uaddr2 or is |
| * waiting on it. If the former, then the pi_state will not |
| * exist yet, look it up one more time to ensure we have a |
| * reference to it. If the lock was taken, ret contains the |
| * vpid of the top waiter task. |
| * If the lock was not taken, we have pi_state and an initial |
| * refcount on it. In case of an error we have nothing. |
| */ |
| if (ret > 0) { |
| WARN_ON(pi_state); |
| drop_count++; |
| task_count++; |
| /* |
| * If we acquired the lock, then the user space value |
| * of uaddr2 should be vpid. It cannot be changed by |
| * the top waiter as it is blocked on hb2 lock if it |
| * tries to do so. If something fiddled with it behind |
| * our back the pi state lookup might unearth it. So |
| * we rather use the known value than rereading and |
| * handing potential crap to lookup_pi_state. |
| * |
| * If that call succeeds then we have pi_state and an |
| * initial refcount on it. |
| */ |
| ret = lookup_pi_state(ret, hb2, &key2, &pi_state); |
| } |
| |
| switch (ret) { |
| case 0: |
| /* We hold a reference on the pi state. */ |
| break; |
| |
| /* If the above failed, then pi_state is NULL */ |
| case -EFAULT: |
| double_unlock_hb(hb1, hb2); |
| hb_waiters_dec(hb2); |
| put_futex_key(&key2); |
| put_futex_key(&key1); |
| ret = fault_in_user_writeable(uaddr2); |
| if (!ret) |
| goto retry; |
| goto out; |
| case -EAGAIN: |
| /* |
| * Two reasons for this: |
| * - Owner is exiting and we just wait for the |
| * exit to complete. |
| * - The user space value changed. |
| */ |
| double_unlock_hb(hb1, hb2); |
| hb_waiters_dec(hb2); |
| put_futex_key(&key2); |
| put_futex_key(&key1); |
| cond_resched(); |
| goto retry; |
| default: |
| goto out_unlock; |
| } |
| } |
| |
| plist_for_each_entry_safe(this, next, &hb1->chain, list) { |
| if (task_count - nr_wake >= nr_requeue) |
| break; |
| |
| if (!match_futex(&this->key, &key1)) |
| continue; |
| |
| /* |
| * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always |
| * be paired with each other and no other futex ops. |
| * |
| * We should never be requeueing a futex_q with a pi_state, |
| * which is awaiting a futex_unlock_pi(). |
| */ |
| if ((requeue_pi && !this->rt_waiter) || |
| (!requeue_pi && this->rt_waiter) || |
| this->pi_state) { |
| ret = -EINVAL; |
| break; |
| } |
| |
| /* |
| * Wake nr_wake waiters. For requeue_pi, if we acquired the |
| * lock, we already woke the top_waiter. If not, it will be |
| * woken by futex_unlock_pi(). |
| */ |
| if (++task_count <= nr_wake && !requeue_pi) { |
| mark_wake_futex(&wake_q, this); |
| continue; |
| } |
| |
| /* Ensure we requeue to the expected futex for requeue_pi. */ |
| if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { |
| ret = -EINVAL; |
| break; |
| } |
| |
| /* |
| * Requeue nr_requeue waiters and possibly one more in the case |
| * of requeue_pi if we couldn't acquire the lock atomically. |
| */ |
| if (requeue_pi) { |
| /* |
| * Prepare the waiter to take the rt_mutex. Take a |
| * refcount on the pi_state and store the pointer in |
| * the futex_q object of the waiter. |
| */ |
| atomic_inc(&pi_state->refcount); |
| this->pi_state = pi_state; |
| ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, |
| this->rt_waiter, |
| this->task); |
| if (ret == 1) { |
| /* |
| * We got the lock. We do neither drop the |
| * refcount on pi_state nor clear |
| * this->pi_state because the waiter needs the |
| * pi_state for cleaning up the user space |
| * value. It will drop the refcount after |
| * doing so. |
| */ |
| requeue_pi_wake_futex(this, &key2, hb2); |
| drop_count++; |
| continue; |
| } else if (ret) { |
| /* |
| * rt_mutex_start_proxy_lock() detected a |
| * potential deadlock when we tried to queue |
| * that waiter. Drop the pi_state reference |
| * which we took above and remove the pointer |
| * to the state from the waiters futex_q |
| * object. |
| */ |
| this->pi_state = NULL; |
| put_pi_state(pi_state); |
| /* |
| * We stop queueing more waiters and let user |
| * space deal with the mess. |
| */ |
| break; |
| } |
| } |
| requeue_futex(this, hb1, hb2, &key2); |
| drop_count++; |
| } |
| |
| /* |
| * We took an extra initial reference to the pi_state either |
| * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We |
| * need to drop it here again. |
| */ |
| put_pi_state(pi_state); |
| |
| out_unlock: |
| double_unlock_hb(hb1, hb2); |
| wake_up_q(&wake_q); |
| hb_waiters_dec(hb2); |
| |
| /* |
| * drop_futex_key_refs() must be called outside the spinlocks. During |
| * the requeue we moved futex_q's from the hash bucket at key1 to the |
| * one at key2 and updated their key pointer. We no longer need to |
| * hold the references to key1. |
| */ |
| while (--drop_count >= 0) |
| drop_futex_key_refs(&key1); |
| |
| out_put_keys: |
| put_futex_key(&key2); |
| out_put_key1: |
| put_futex_key(&key1); |
| out: |
| return ret ? ret : task_count; |
| } |
| |
| /* The key must be already stored in q->key. */ |
| static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) |
| __acquires(&hb->lock) |
| { |
| struct futex_hash_bucket *hb; |
| |
| hb = hash_futex(&q->key); |
| |
| /* |
| * Increment the counter before taking the lock so that |
| * a potential waker won't miss a to-be-slept task that is |
| * waiting for the spinlock. This is safe as all queue_lock() |
| * users end up calling queue_me(). Similarly, for housekeeping, |
| * decrement the counter at queue_unlock() when some error has |
| * occurred and we don't end up adding the task to the list. |
| */ |
| hb_waiters_inc(hb); |
| |
| q->lock_ptr = &hb->lock; |
| |
| spin_lock(&hb->lock); /* implies smp_mb(); (A) */ |
| return hb; |
| } |
| |
| static inline void |
| queue_unlock(struct futex_hash_bucket *hb) |
| __releases(&hb->lock) |
| { |
| spin_unlock(&hb->lock); |
| hb_waiters_dec(hb); |
| } |
| |
| /** |
| * queue_me() - Enqueue the futex_q on the futex_hash_bucket |
| * @q: The futex_q to enqueue |
| * @hb: The destination hash bucket |
| * |
| * The hb->lock must be held by the caller, and is released here. A call to |
| * queue_me() is typically paired with exactly one call to unqueue_me(). The |
| * exceptions involve the PI related operations, which may use unqueue_me_pi() |
| * or nothing if the unqueue is done as part of the wake process and the unqueue |
| * state is implicit in the state of woken task (see futex_wait_requeue_pi() for |
| * an example). |
| */ |
| static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
| __releases(&hb->lock) |
| { |
| int prio; |
| |
| /* |
| * The priority used to register this element is |
| * - either the real thread-priority for the real-time threads |
| * (i.e. threads with a priority lower than MAX_RT_PRIO) |
| * - or MAX_RT_PRIO for non-RT threads. |
| * Thus, all RT-threads are woken first in priority order, and |
| * the others are woken last, in FIFO order. |
| */ |
| prio = min(current->normal_prio, MAX_RT_PRIO); |
| |
| plist_node_init(&q->list, prio); |
| plist_add(&q->list, &hb->chain); |
| q->task = current; |
| spin_unlock(&hb->lock); |
| } |
| |
| /** |
| * unqueue_me() - Remove the futex_q from its futex_hash_bucket |
| * @q: The futex_q to unqueue |
| * |
| * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must |
| * be paired with exactly one earlier call to queue_me(). |
| * |
| * Return: |
| * 1 - if the futex_q was still queued (and we removed unqueued it); |
| * 0 - if the futex_q was already removed by the waking thread |
| */ |
| static int unqueue_me(struct futex_q *q) |
| { |
| spinlock_t *lock_ptr; |
| int ret = 0; |
| |
| /* In the common case we don't take the spinlock, which is nice. */ |
| retry: |
| /* |
| * q->lock_ptr can change between this read and the following spin_lock. |
| * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and |
| * optimizing lock_ptr out of the logic below. |
| */ |
| lock_ptr = READ_ONCE(q->lock_ptr); |
| if (lock_ptr != NULL) { |
| spin_lock(lock_ptr); |
| /* |
| * q->lock_ptr can change between reading it and |
| * spin_lock(), causing us to take the wrong lock. This |
| * corrects the race condition. |
| * |
| * Reasoning goes like this: if we have the wrong lock, |
| * q->lock_ptr must have changed (maybe several times) |
| * between reading it and the spin_lock(). It can |
| * change again after the spin_lock() but only if it was |
| * already changed before the spin_lock(). It cannot, |
| * however, change back to the original value. Therefore |
| * we can detect whether we acquired the correct lock. |
| */ |
| if (unlikely(lock_ptr != q->lock_ptr)) { |
| spin_unlock(lock_ptr); |
| goto retry; |
| } |
| __unqueue_futex(q); |
| |
| BUG_ON(q->pi_state); |
| |
| spin_unlock(lock_ptr); |
| ret = 1; |
| } |
| |
| drop_futex_key_refs(&q->key); |
| return ret; |
| } |
| |
| /* |
| * PI futexes can not be requeued and must remove themself from the |
| * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry |
| * and dropped here. |
| */ |
| static void unqueue_me_pi(struct futex_q *q) |
| __releases(q->lock_ptr) |
| { |
| __unqueue_futex(q); |
| |
| BUG_ON(!q->pi_state); |
| put_pi_state(q->pi_state); |
| q->pi_state = NULL; |
| |
| spin_unlock(q->lock_ptr); |
| } |
| |
| /* |
| * Fixup the pi_state owner with the new owner. |
| * |
| * Must be called with hash bucket lock held and mm->sem held for non |
| * private futexes. |
| */ |
| static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
| struct task_struct *newowner) |
| { |
| u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; |
| struct futex_pi_state *pi_state = q->pi_state; |
| struct task_struct *oldowner = pi_state->owner; |
| u32 uval, uninitialized_var(curval), newval; |
| int ret; |
| |
| /* Owner died? */ |
| if (!pi_state->owner) |
| newtid |= FUTEX_OWNER_DIED; |
| |
| /* |
| * We are here either because we stole the rtmutex from the |
| * previous highest priority waiter or we are the highest priority |
| * waiter but failed to get the rtmutex the first time. |
| * We have to replace the newowner TID in the user space variable. |
| * This must be atomic as we have to preserve the owner died bit here. |
| * |
| * Note: We write the user space value _before_ changing the pi_state |
| * because we can fault here. Imagine swapped out pages or a fork |
| * that marked all the anonymous memory readonly for cow. |
| * |
| * Modifying pi_state _before_ the user space value would |
| * leave the pi_state in an inconsistent state when we fault |
| * here, because we need to drop the hash bucket lock to |
| * handle the fault. This might be observed in the PID check |
| * in lookup_pi_state. |
| */ |
| retry: |
| if (get_futex_value_locked(&uval, uaddr)) |
| goto handle_fault; |
| |
| while (1) { |
| newval = (uval & FUTEX_OWNER_DIED) | newtid; |
| |
| if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
| goto handle_fault; |
| if (curval == uval) |
| break; |
| uval = curval; |
| } |
| |
| /* |
| * We fixed up user space. Now we need to fix the pi_state |
| * itself. |
| */ |
| if (pi_state->owner != NULL) { |
| raw_spin_lock_irq(&pi_state->owner->pi_lock); |
| WARN_ON(list_empty(&pi_state->list)); |
| list_del_init(&pi_state->list); |
| raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
| } |
| |
| pi_state->owner = newowner; |
| |
| raw_spin_lock_irq(&newowner->pi_lock); |
| WARN_ON(!list_empty(&pi_state->list)); |
| list_add(&pi_state->list, &newowner->pi_state_list); |
| raw_spin_unlock_irq(&newowner->pi_lock); |
| return 0; |
| |
| /* |
| * To handle the page fault we need to drop the hash bucket |
| * lock here. That gives the other task (either the highest priority |
| * waiter itself or the task which stole the rtmutex) the |
| * chance to try the fixup of the pi_state. So once we are |
| * back from handling the fault we need to check the pi_state |
| * after reacquiring the hash bucket lock and before trying to |
| * do another fixup. When the fixup has been done already we |
| * simply return. |
| */ |
| handle_fault: |
| spin_unlock(q->lock_ptr); |
| |
| ret = fault_in_user_writeable(uaddr); |
| |
| spin_lock(q->lock_ptr); |
| |
| /* |
| * Check if someone else fixed it for us: |
| */ |
| if (pi_state->owner != oldowner) |
| return 0; |
| |
| if (ret) |
| return ret; |
| |
| goto retry; |
| } |
| |
| static long futex_wait_restart(struct restart_block *restart); |
| |
| /** |
| * fixup_owner() - Post lock pi_state and corner case management |
| * @uaddr: user address of the futex |
| * @q: futex_q (contains pi_state and access to the rt_mutex) |
| * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) |
| * |
| * After attempting to lock an rt_mutex, this function is called to cleanup |
| * the pi_state owner as well as handle race conditions that may allow us to |
| * acquire the lock. Must be called with the hb lock held. |
| * |
| * Return: |
| * 1 - success, lock taken; |
| * 0 - success, lock not taken; |
| * <0 - on error (-EFAULT) |
| */ |
| static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) |
| { |
| struct task_struct *owner; |
| int ret = 0; |
| |
| if (locked) { |
| /* |
| * Got the lock. We might not be the anticipated owner if we |
| * did a lock-steal - fix up the PI-state in that case: |
| */ |
| if (q->pi_state->owner != current) |
| ret = fixup_pi_state_owner(uaddr, q, current); |
| goto out; |
| } |
| |
| /* |
| * Catch the rare case, where the lock was released when we were on the |
| * way back before we locked the hash bucket. |
| */ |
| if (q->pi_state->owner == current) { |
| /* |
| * Try to get the rt_mutex now. This might fail as some other |
| * task acquired the rt_mutex after we removed ourself from the |
| * rt_mutex waiters list. |
| */ |
| if (rt_mutex_trylock(&q->pi_state->pi_mutex)) { |
| locked = 1; |
| goto out; |
| } |
| |
| /* |
| * pi_state is incorrect, some other task did a lock steal and |
| * we returned due to timeout or signal without taking the |
| * rt_mutex. Too late. |
| */ |
| raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock); |
| owner = rt_mutex_owner(&q->pi_state->pi_mutex); |
| if (!owner) |
| owner = rt_mutex_next_owner(&q->pi_state->pi_mutex); |
| raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock); |
| ret = fixup_pi_state_owner(uaddr, q, owner); |
| goto out; |
| } |
| |
| /* |
| * Paranoia check. If we did not take the lock, then we should not be |
| * the owner of the rt_mutex. |
| */ |
| if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) |
| printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " |
| "pi-state %p\n", ret, |
| q->pi_state->pi_mutex.owner, |
| q->pi_state->owner); |
| |
| out: |
| return ret ? ret : locked; |
| } |
| |
| /** |
| * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal |
| * @hb: the futex hash bucket, must be locked by the caller |
| * @q: the futex_q to queue up on |
| * @timeout: the prepared hrtimer_sleeper, or null for no timeout |
| */ |
| static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, |
| struct hrtimer_sleeper *timeout) |
| { |
| /* |
| * The task state is guaranteed to be set before another task can |
| * wake it. set_current_state() is implemented using smp_store_mb() and |
| * queue_me() calls spin_unlock() upon completion, both serializing |
| * access to the hash list and forcing another memory barrier. |
| */ |
| set_current_state(TASK_INTERRUPTIBLE); |
| queue_me(q, hb); |
| |
| /* Arm the timer */ |
| if (timeout) |
| hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); |
| |
| /* |
| * If we have been removed from the hash list, then another task |
| * has tried to wake us, and we can skip the call to schedule(). |
| */ |
| if (likely(!plist_node_empty(&q->list))) { |
| /* |
| * If the timer has already expired, current will already be |
| * flagged for rescheduling. Only call schedule if there |
| * is no timeout, or if it has yet to expire. |
| */ |
| if (!timeout || timeout->task) |
| freezable_schedule(); |
| } |
| __set_current_state(TASK_RUNNING); |
| } |
| |
| /** |
| * futex_wait_setup() - Prepare to wait on a futex |
| * @uaddr: the futex userspace address |
| * @val: the expected value |
| * @flags: futex flags (FLAGS_SHARED, etc.) |
| * @q: the associated futex_q |
| * @hb: storage for hash_bucket pointer to be returned to caller |
| * |
| * Setup the futex_q and locate the hash_bucket. Get the futex value and |
| * compare it with the expected value. Handle atomic faults internally. |
| * Return with the hb lock held and a q.key reference on success, and unlocked |
| * with no q.key reference on failure. |
| * |
| * Return: |
| * 0 - uaddr contains val and hb has been locked; |
| * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked |
| */ |
| static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, |
| struct futex_q *q, struct futex_hash_bucket **hb) |
| { |
| u32 uval; |
| int ret; |
| |
| /* |
| * Access the page AFTER the hash-bucket is locked. |
| * Order is important: |
| * |
| * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); |
| * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } |
| * |
| * The basic logical guarantee of a futex is that it blocks ONLY |
| * if cond(var) is known to be true at the time of blocking, for |
| * any cond. If we locked the hash-bucket after testing *uaddr, that |
| * would open a race condition where we could block indefinitely with |
| * cond(var) false, which would violate the guarantee. |
| * |
| * On the other hand, we insert q and release the hash-bucket only |
| * after testing *uaddr. This guarantees that futex_wait() will NOT |
| * absorb a wakeup if *uaddr does not match the desired values |
| * while the syscall executes. |
| */ |
| retry: |
| ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ); |
| if (unlikely(ret != 0)) |
| return ret; |
| |
| retry_private: |
| *hb = queue_lock(q); |
| |
| ret = get_futex_value_locked(&uval, uaddr); |
| |
| if (ret) { |
| queue_unlock(*hb); |
| |
| ret = get_user(uval, uaddr); |
| if (ret) |
| goto out; |
| |
| if (!(flags & FLAGS_SHARED)) |
| goto retry_private; |
| |
| put_futex_key(&q->key); |
| goto retry; |
| } |
| |
| if (uval != val) { |
| queue_unlock(*hb); |
| ret = -EWOULDBLOCK; |
| } |
| |
| out: |
| if (ret) |
| put_futex_key(&q->key); |
| return ret; |
| } |
| |
| static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, |
| ktime_t *abs_time, u32 bitset) |
| { |
| struct hrtimer_sleeper timeout, *to = NULL; |
| struct restart_block *restart; |
| struct futex_hash_bucket *hb; |
| struct futex_q q = futex_q_init; |
| int ret; |
| |
| if (!bitset) |
| return -EINVAL; |
| q.bitset = bitset; |
| |
| if (abs_time) { |
| to = &timeout; |
| |
| hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
| CLOCK_REALTIME : CLOCK_MONOTONIC, |
| HRTIMER_MODE_ABS); |
| hrtimer_init_sleeper(to, current); |
| hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
| current->timer_slack_ns); |
| } |
| |
| retry: |
| /* |
| * Prepare to wait on uaddr. On success, holds hb lock and increments |
| * q.key refs. |
| */ |
| ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
| if (ret) |
| goto out; |
| |
| /* queue_me and wait for wakeup, timeout, or a signal. */ |
| futex_wait_queue_me(hb, &q, to); |
| |
| /* If we were woken (and unqueued), we succeeded, whatever. */ |
| ret = 0; |
| /* unqueue_me() drops q.key ref */ |
| if (!unqueue_me(&q)) |
| goto out; |
| ret = -ETIMEDOUT; |
| if (to && !to->task) |
| goto out; |
| |
| /* |
| * We expect signal_pending(current), but we might be the |
| * victim of a spurious wakeup as well. |
| */ |
| if (!signal_pending(current)) |
| goto retry; |
| |
| ret = -ERESTARTSYS; |
| if (!abs_time) |
| goto out; |
| |
| restart = ¤t->restart_block; |
| restart->fn = futex_wait_restart; |
| restart->futex.uaddr = uaddr; |
| restart->futex.val = val; |
| restart->futex.time = *abs_time; |
| restart->futex.bitset = bitset; |
| restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; |
| |
| ret = -ERESTART_RESTARTBLOCK; |
| |
| out: |
| if (to) { |
| hrtimer_cancel(&to->timer); |
| destroy_hrtimer_on_stack(&to->timer); |
| } |
| return ret; |
| } |
| |
| |
| static long futex_wait_restart(struct restart_block *restart) |
| { |
| u32 __user *uaddr = restart->futex.uaddr; |
| ktime_t t, *tp = NULL; |
| |
| if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { |
| t = restart->futex.time; |
| tp = &t; |
| } |
| restart->fn = do_no_restart_syscall; |
| |
| return (long)futex_wait(uaddr, restart->futex.flags, |
| restart->futex.val, tp, restart->futex.bitset); |
| } |
| |
| |
| /* |
| * Userspace tried a 0 -> TID atomic transition of the futex value |
| * and failed. The kernel side here does the whole locking operation: |
| * if there are waiters then it will block as a consequence of relying |
| * on rt-mutexes, it does PI, etc. (Due to races the kernel might see |
| * a 0 value of the futex too.). |
| * |
| * Also serves as futex trylock_pi()'ing, and due semantics. |
| */ |
| static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, |
| ktime_t *time, int trylock) |
| { |
| struct hrtimer_sleeper timeout, *to = NULL; |
| struct futex_hash_bucket *hb; |
| struct futex_q q = futex_q_init; |
| int res, ret; |
| |
| if (refill_pi_state_cache()) |
| return -ENOMEM; |
| |
| if (time) { |
| to = &timeout; |
| hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, |
| HRTIMER_MODE_ABS); |
| hrtimer_init_sleeper(to, current); |
| hrtimer_set_expires(&to->timer, *time); |
| } |
| |
| retry: |
| ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE); |
| if (unlikely(ret != 0)) |
| goto out; |
| |
| retry_private: |
| hb = queue_lock(&q); |
| |
| ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); |
| if (unlikely(ret)) { |
| /* |
| * Atomic work succeeded and we got the lock, |
| * or failed. Either way, we do _not_ block. |
| */ |
| switch (ret) { |
| case 1: |
| /* We got the lock. */ |
| ret = 0; |
| goto out_unlock_put_key; |
| case -EFAULT: |
| goto uaddr_faulted; |
| case -EAGAIN: |
| /* |
| * Two reasons for this: |
| * - Task is exiting and we just wait for the |
| * exit to complete. |
| * - The user space value changed. |
| */ |
| queue_unlock(hb); |
| put_futex_key(&q.key); |
| cond_resched(); |
| goto retry; |
| default: |
| goto out_unlock_put_key; |
| } |
| } |
| |
| /* |
| * Only actually queue now that the atomic ops are done: |
| */ |
| queue_me(&q, hb); |
| |
| WARN_ON(!q.pi_state); |
| /* |
| * Block on the PI mutex: |
| */ |
| if (!trylock) { |
| ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to); |
| } else { |
| ret = rt_mutex_trylock(&q.pi_state->pi_mutex); |
| /* Fixup the trylock return value: */ |
| ret = ret ? 0 : -EWOULDBLOCK; |
| } |
| |
| spin_lock(q.lock_ptr); |
| /* |
| * Fixup the pi_state owner and possibly acquire the lock if we |
| * haven't already. |
| */ |
| res = fixup_owner(uaddr, &q, !ret); |
| /* |
| * If fixup_owner() returned an error, proprogate that. If it acquired |
| * the lock, clear our -ETIMEDOUT or -EINTR. |
| */ |
| if (res) |
| ret = (res < 0) ? res : 0; |
| |
| /* |
| * If fixup_owner() faulted and was unable to handle the fault, unlock |
| * it and return the fault to userspace. |
| */ |
| if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) |
| rt_mutex_unlock(&q.pi_state->pi_mutex); |
| |
| /* Unqueue and drop the lock */ |
| unqueue_me_pi(&q); |
| |
| goto out_put_key; |
| |
| out_unlock_put_key: |
| queue_unlock(hb); |
| |
| out_put_key: |
| put_futex_key(&q.key); |
| out: |
| if (to) |
| destroy_hrtimer_on_stack(&to->timer); |
| return ret != -EINTR ? ret : -ERESTARTNOINTR; |
| |
| uaddr_faulted: |
| queue_unlock(hb); |
| |
| ret = fault_in_user_writeable(uaddr); |
| if (ret) |
| goto out_put_key; |
| |
| if (!(flags & FLAGS_SHARED)) |
| goto retry_private; |
| |
| put_futex_key(&q.key); |
| goto retry; |
| } |
| |
| /* |
| * Userspace attempted a TID -> 0 atomic transition, and failed. |
| * This is the in-kernel slowpath: we look up the PI state (if any), |
| * and do the rt-mutex unlock. |
| */ |
| static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) |
| { |
| u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current); |
| union futex_key key = FUTEX_KEY_INIT; |
| struct futex_hash_bucket *hb; |
| struct futex_q *match; |
| int ret; |
| |
| retry: |
| if (get_user(uval, uaddr)) |
| return -EFAULT; |
| /* |
| * We release only a lock we actually own: |
| */ |
| if ((uval & FUTEX_TID_MASK) != vpid) |
| return -EPERM; |
| |
| ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE); |
| if (ret) |
| return ret; |
| |
| hb = hash_futex(&key); |
| spin_lock(&hb->lock); |
| |
| /* |
| * Check waiters first. We do not trust user space values at |
| * all and we at least want to know if user space fiddled |
| * with the futex value instead of blindly unlocking. |
| */ |
| match = futex_top_waiter(hb, &key); |
| if (match) { |
| ret = wake_futex_pi(uaddr, uval, match, hb); |
| /* |
| * In case of success wake_futex_pi dropped the hash |
| * bucket lock. |
| */ |
| if (!ret) |
| goto out_putkey; |
| /* |
| * The atomic access to the futex value generated a |
| * pagefault, so retry the user-access and the wakeup: |
| */ |
| if (ret == -EFAULT) |
| goto pi_faulted; |
| /* |
| * A unconditional UNLOCK_PI op raced against a waiter |
| * setting the FUTEX_WAITERS bit. Try again. |
| */ |
| if (ret == -EAGAIN) { |
| spin_unlock(&hb->lock); |
| put_futex_key(&key); |
| goto retry; |
| } |
| /* |
| * wake_futex_pi has detected invalid state. Tell user |
| * space. |
| */ |
| goto out_unlock; |
| } |
| |
| /* |
| * We have no kernel internal state, i.e. no waiters in the |
| * kernel. Waiters which are about to queue themselves are stuck |
| * on hb->lock. So we can safely ignore them. We do neither |
| * preserve the WAITERS bit not the OWNER_DIED one. We are the |
| * owner. |
| */ |
| if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) |
| goto pi_faulted; |
| |
| /* |
| * If uval has changed, let user space handle it. |
| */ |
| ret = (curval == uval) ? 0 : -EAGAIN; |
| |
| out_unlock: |
| spin_unlock(&hb->lock); |
| out_putkey: |
| put_futex_key(&key); |
| return ret; |
| |
| pi_faulted: |
| spin_unlock(&hb->lock); |
| put_futex_key(&key); |
| |
| ret = fault_in_user_writeable(uaddr); |
| if (!ret) |
| goto retry; |
| |
| return ret; |
| } |
| |
| /** |
| * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex |
| * @hb: the hash_bucket futex_q was original enqueued on |
| * @q: the futex_q woken while waiting to be requeued |
| * @key2: the futex_key of the requeue target futex |
| * @timeout: the timeout associated with the wait (NULL if none) |
| * |
| * Detect if the task was woken on the initial futex as opposed to the requeue |
| * target futex. If so, determine if it was a timeout or a signal that caused |
| * the wakeup and return the appropriate error code to the caller. Must be |
| * called with the hb lock held. |
| * |
| * Return: |
| * 0 = no early wakeup detected; |
| * <0 = -ETIMEDOUT or -ERESTARTNOINTR |
| */ |
| static inline |
| int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, |
| struct futex_q *q, union futex_key *key2, |
| struct hrtimer_sleeper *timeout) |
| { |
| int ret = 0; |
| |
| /* |
| * With the hb lock held, we avoid races while we process the wakeup. |
| * We only need to hold hb (and not hb2) to ensure atomicity as the |
| * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. |
| * It can't be requeued from uaddr2 to something else since we don't |
| * support a PI aware source futex for requeue. |
| */ |
| if (!match_futex(&q->key, key2)) { |
| WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); |
| /* |
| * We were woken prior to requeue by a timeout or a signal. |
| * Unqueue the futex_q and determine which it was. |
| */ |
| plist_del(&q->list, &hb->chain); |
| hb_waiters_dec(hb); |
| |
| /* Handle spurious wakeups gracefully */ |
| ret = -EWOULDBLOCK; |
| if (timeout && !timeout->task) |
| ret = -ETIMEDOUT; |
| else if (signal_pending(current)) |
| ret = -ERESTARTNOINTR; |
| } |
| return ret; |
| } |
| |
| /** |
| * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 |
| * @uaddr: the futex we initially wait on (non-pi) |
| * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be |
| * the same type, no requeueing from private to shared, etc. |
| * @val: the expected value of uaddr |
| * @abs_time: absolute timeout |
| * @bitset: 32 bit wakeup bitset set by userspace, defaults to all |
| * @uaddr2: the pi futex we will take prior to returning to user-space |
| * |
| * The caller will wait on uaddr and will be requeued by futex_requeue() to |
| * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake |
| * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to |
| * userspace. This ensures the rt_mutex maintains an owner when it has waiters; |
| * without one, the pi logic would not know which task to boost/deboost, if |
| * there was a need to. |
| * |
| * We call schedule in futex_wait_queue_me() when we enqueue and return there |
| * via the following-- |
| * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
| * 2) wakeup on uaddr2 after a requeue |
| * 3) signal |
| * 4) timeout |
| * |
| * If 3, cleanup and return -ERESTARTNOINTR. |
| * |
| * If 2, we may then block on trying to take the rt_mutex and return via: |
| * 5) successful lock |
| * 6) signal |
| * 7) timeout |
| * 8) other lock acquisition failure |
| * |
| * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). |
| * |
| * If 4 or 7, we cleanup and return with -ETIMEDOUT. |
| * |
| * Return: |
| * 0 - On success; |
| * <0 - On error |
| */ |
| static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, |
| u32 val, ktime_t *abs_time, u32 bitset, |
| u32 __user *uaddr2) |
| { |
| struct hrtimer_sleeper timeout, *to = NULL; |
| struct rt_mutex_waiter rt_waiter; |
| struct rt_mutex *pi_mutex = NULL; |
| struct futex_hash_bucket *hb; |
| union futex_key key2 = FUTEX_KEY_INIT; |
| struct futex_q q = futex_q_init; |
| int res, ret; |
| |
| if (uaddr == uaddr2) |
| return -EINVAL; |
| |
| if (!bitset) |
| return -EINVAL; |
| |
| if (abs_time) { |
| to = &timeout; |
| hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
| CLOCK_REALTIME : CLOCK_MONOTONIC, |
| HRTIMER_MODE_ABS); |
| hrtimer_init_sleeper(to, current); |
| hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
| current->timer_slack_ns); |
| } |
| |
| /* |
| * The waiter is allocated on our stack, manipulated by the requeue |
| * code while we sleep on uaddr. |
| */ |
| debug_rt_mutex_init_waiter(&rt_waiter); |
| RB_CLEAR_NODE(&rt_waiter.pi_tree_entry); |
| RB_CLEAR_NODE(&rt_waiter.tree_entry); |
| rt_waiter.task = NULL; |
| |
| ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
| if (unlikely(ret != 0)) |
| goto out; |
| |
| q.bitset = bitset; |
| q.rt_waiter = &rt_waiter; |
| q.requeue_pi_key = &key2; |
| |
| /* |
| * Prepare to wait on uaddr. On success, increments q.key (key1) ref |
| * count. |
| */ |
| ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
| if (ret) |
| goto out_key2; |
| |
| /* |
| * The check above which compares uaddrs is not sufficient for |
| * shared futexes. We need to compare the keys: |
| */ |
| if (match_futex(&q.key, &key2)) { |
| queue_unlock(hb); |
| ret = -EINVAL; |
| goto out_put_keys; |
| } |
| |
| /* Queue the futex_q, drop the hb lock, wait for wakeup. */ |
| futex_wait_queue_me(hb, &q, to); |
| |
| spin_lock(&hb->lock); |
| ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); |
| spin_unlock(&hb->lock); |
| if (ret) |
| goto out_put_keys; |
| |
| /* |
| * In order for us to be here, we know our q.key == key2, and since |
| * we took the hb->lock above, we also know that futex_requeue() has |
| * completed and we no longer have to concern ourselves with a wakeup |
| * race with the atomic proxy lock acquisition by the requeue code. The |
| * futex_requeue dropped our key1 reference and incremented our key2 |
| * reference count. |
| */ |
| |
| /* Check if the requeue code acquired the second futex for us. */ |
| if (!q.rt_waiter) { |
| /* |
| * Got the lock. We might not be the anticipated owner if we |
| * did a lock-steal - fix up the PI-state in that case. |
| */ |
| if (q.pi_state && (q.pi_state->owner != current)) { |
| spin_lock(q.lock_ptr); |
| ret = fixup_pi_state_owner(uaddr2, &q, current); |
| /* |
| * Drop the reference to the pi state which |
| * the requeue_pi() code acquired for us. |
| */ |
| put_pi_state(q.pi_state); |
| spin_unlock(q.lock_ptr); |
| } |
| } else { |
| /* |
| * We have been woken up by futex_unlock_pi(), a timeout, or a |
| * signal. futex_unlock_pi() will not destroy the lock_ptr nor |
| * the pi_state. |
| */ |
| WARN_ON(!q.pi_state); |
| pi_mutex = &q.pi_state->pi_mutex; |
| ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter); |
| debug_rt_mutex_free_waiter(&rt_waiter); |
| |
| spin_lock(q.lock_ptr); |
| /* |
| * Fixup the pi_state owner and possibly acquire the lock if we |
| * haven't already. |
| */ |
| res = fixup_owner(uaddr2, &q, !ret); |
| /* |
| * If fixup_owner() returned an error, proprogate that. If it |
| * acquired the lock, clear -ETIMEDOUT or -EINTR. |
| */ |
| if (res) |
| ret = (res < 0) ? res : 0; |
| |
| /* Unqueue and drop the lock. */ |
| unqueue_me_pi(&q); |
| } |
| |
| /* |
| * If fixup_pi_state_owner() faulted and was unable to handle the |
| * fault, unlock the rt_mutex and return the fault to userspace. |
| */ |
| if (ret == -EFAULT) { |
| if (pi_mutex && rt_mutex_owner(pi_mutex) == current) |
| rt_mutex_unlock(pi_mutex); |
| } else if (ret == -EINTR) { |
| /* |
| * We've already been requeued, but cannot restart by calling |
| * futex_lock_pi() directly. We could restart this syscall, but |
| * it would detect that the user space "val" changed and return |
| * -EWOULDBLOCK. Save the overhead of the restart and return |
| * -EWOULDBLOCK directly. |
| */ |
| ret = -EWOULDBLOCK; |
| } |
| |
| out_put_keys: |
| put_futex_key(&q.key); |
| out_key2: |
| put_futex_key(&key2); |
| |
| out: |
| if (to) { |
| hrtimer_cancel(&to->timer); |
| destroy_hrtimer_on_stack(&to->timer); |
| } |
| return ret; |
| } |
| |
| /* |
| * Support for robust futexes: the kernel cleans up held futexes at |
| * thread exit time. |
| * |
| * Implementation: user-space maintains a per-thread list of locks it |
| * is holding. Upon do_exit(), the kernel carefully walks this list, |
| * and marks all locks that are owned by this thread with the |
| * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is |
| * always manipulated with the lock held, so the list is private and |
| * per-thread. Userspace also maintains a per-thread 'list_op_pending' |
| * field, to allow the kernel to clean up if the thread dies after |
| * acquiring the lock, but just before it could have added itself to |
| * the list. There can only be one such pending lock. |
| */ |
| |
| /** |
| * sys_set_robust_list() - Set the robust-futex list head of a task |
| * @head: pointer to the list-head |
| * @len: length of the list-head, as userspace expects |
| */ |
| SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, |
| size_t, len) |
| { |
| if (!futex_cmpxchg_enabled) |
| return -ENOSYS; |
| /* |
| * The kernel knows only one size for now: |
| */ |
| if (unlikely(len != sizeof(*head))) |
| return -EINVAL; |
| |
| current->robust_list = head; |
| |
| return 0; |
| } |
| |
| /** |
| * sys_get_robust_list() - Get the robust-futex list head of a task |
| * @pid: pid of the process [zero for current task] |
| * @head_ptr: pointer to a list-head pointer, the kernel fills it in |
| * @len_ptr: pointer to a length field, the kernel fills in the header size |
| */ |
| SYSCALL_DEFINE3(get_robust_list, int, pid, |
| struct robust_list_head __user * __user *, head_ptr, |
| size_t __user *, len_ptr) |
| { |
| struct robust_list_head __user *head; |
| unsigned long ret; |
| struct task_struct *p; |
| |
| if (!futex_cmpxchg_enabled) |
| return -ENOSYS; |
| |
| rcu_read_lock(); |
| |
| ret = -ESRCH; |
| if (!pid) |
| p = current; |
| else { |
| p = find_task_by_vpid(pid); |
| if (!p) |
| goto err_unlock; |
| } |
| |
| ret = -EPERM; |
| if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) |
| goto err_unlock; |
| |
| head = p->robust_list; |
| rcu_read_unlock(); |
| |
| if (put_user(sizeof(*head), len_ptr)) |
| return -EFAULT; |
| return put_user(head, head_ptr); |
| |
| err_unlock: |
| rcu_read_unlock(); |
| |
| return ret; |
| } |
| |
| /* |
| * Process a futex-list entry, check whether it's owned by the |
| * dying task, and do notification if so: |
| */ |
| int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) |
| { |
| u32 uval, uninitialized_var(nval), mval; |
| |
| retry: |
| if (get_user(uval, uaddr)) |
| return -1; |
| |
| if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { |
| /* |
| * Ok, this dying thread is truly holding a futex |
| * of interest. Set the OWNER_DIED bit atomically |
| * via cmpxchg, and if the value had FUTEX_WAITERS |
| * set, wake up a waiter (if any). (We have to do a |
| * futex_wake() even if OWNER_DIED is already set - |
| * to handle the rare but possible case of recursive |
| * thread-death.) The rest of the cleanup is done in |
| * userspace. |
| */ |
| mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; |
| /* |
| * We are not holding a lock here, but we want to have |
| * the pagefault_disable/enable() protection because |
| * we want to handle the fault gracefully. If the |
| * access fails we try to fault in the futex with R/W |
| * verification via get_user_pages. get_user() above |
| * does not guarantee R/W access. If that fails we |
| * give up and leave the futex locked. |
| */ |
| if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { |
| if (fault_in_user_writeable(uaddr)) |
| return -1; |
| goto retry; |
| } |
| if (nval != uval) |
| goto retry; |
| |
| /* |
| * Wake robust non-PI futexes here. The wakeup of |
| * PI futexes happens in exit_pi_state(): |
| */ |
| if (!pi && (uval & FUTEX_WAITERS)) |
| futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
| } |
| return 0; |
| } |
| |
| /* |
| * Fetch a robust-list pointer. Bit 0 signals PI futexes: |
| */ |
| static inline int fetch_robust_entry(struct robust_list __user **entry, |
| struct robust_list __user * __user *head, |
| unsigned int *pi) |
| { |
| unsigned long uentry; |
| |
| if (get_user(uentry, (unsigned long __user *)head)) |
| return -EFAULT; |
| |
| *entry = (void __user *)(uentry & ~1UL); |
| *pi = uentry & 1; |
| |
| return 0; |
| } |
| |
| /* |
| * Walk curr->robust_list (very carefully, it's a userspace list!) |
| * and mark any locks found there dead, and notify any waiters. |
| * |
| * We silently return on any sign of list-walking problem. |
| */ |
| void exit_robust_list(struct task_struct *curr) |
| { |
| struct robust_list_head __user *head = curr->robust_list; |
| struct robust_list __user *entry, *next_entry, *pending; |
| unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
| unsigned int uninitialized_var(next_pi); |
| unsigned long futex_offset; |
| int rc; |
| |
| if (!futex_cmpxchg_enabled) |
| return; |
| |
| /* |
| * Fetch the list head (which was registered earlier, via |
| * sys_set_robust_list()): |
| */ |
| if (fetch_robust_entry(&entry, &head->list.next, &pi)) |
| return; |
| /* |
| * Fetch the relative futex offset: |
| */ |
| if (get_user(futex_offset, &head->futex_offset)) |
| return; |
| /* |
| * Fetch any possibly pending lock-add first, and handle it |
| * if it exists: |
| */ |
| if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) |
| return; |
| |
| next_entry = NULL; /* avoid warning with gcc */ |
| while (entry != &head->list) { |
| /* |
| * Fetch the next entry in the list before calling |
| * handle_futex_death: |
| */ |
| rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); |
| /* |
| * A pending lock might already be on the list, so |
| * don't process it twice: |
| */ |
| if (entry != pending) |
| if (handle_futex_death((void __user *)entry + futex_offset, |
| curr, pi)) |
| return; |
| if (rc) |
| return; |
| entry = next_entry; |
| pi = next_pi; |
| /* |
| * Avoid excessively long or circular lists: |
| */ |
| if (!--limit) |
| break; |
| |
| cond_resched(); |
| } |
| |
| if (pending) |
| handle_futex_death((void __user *)pending + futex_offset, |
| curr, pip); |
| } |
| |
| long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, |
| u32 __user *uaddr2, u32 val2, u32 val3) |
| { |
| int cmd = op & FUTEX_CMD_MASK; |
| unsigned int flags = 0; |
| |
| if (!(op & FUTEX_PRIVATE_FLAG)) |
| flags |= FLAGS_SHARED; |
| |
| if (op & FUTEX_CLOCK_REALTIME) { |
| flags |= FLAGS_CLOCKRT; |
| if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ |
| cmd != FUTEX_WAIT_REQUEUE_PI) |
| return -ENOSYS; |
| } |
| |
| switch (cmd) { |
| case FUTEX_LOCK_PI: |
| case FUTEX_UNLOCK_PI: |
| case FUTEX_TRYLOCK_PI: |
| case FUTEX_WAIT_REQUEUE_PI: |
| case FUTEX_CMP_REQUEUE_PI: |
| if (!futex_cmpxchg_enabled) |
| return -ENOSYS; |
| } |
| |
| switch (cmd) { |
| case FUTEX_WAIT: |
| val3 = FUTEX_BITSET_MATCH_ANY; |
| case FUTEX_WAIT_BITSET: |
| return futex_wait(uaddr, flags, val, timeout, val3); |
| case FUTEX_WAKE: |
| val3 = FUTEX_BITSET_MATCH_ANY; |
| case FUTEX_WAKE_BITSET: |
| return futex_wake(uaddr, flags, val, val3); |
| case FUTEX_REQUEUE: |
| return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); |
| case FUTEX_CMP_REQUEUE: |
| return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); |
| case FUTEX_WAKE_OP: |
| return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); |
| case FUTEX_LOCK_PI: |
| return futex_lock_pi(uaddr, flags, timeout, 0); |
| case FUTEX_UNLOCK_PI: |
| return futex_unlock_pi(uaddr, flags); |
| case FUTEX_TRYLOCK_PI: |
| return futex_lock_pi(uaddr, flags, NULL, 1); |
| case FUTEX_WAIT_REQUEUE_PI: |
| val3 = FUTEX_BITSET_MATCH_ANY; |
| return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, |
| uaddr2); |
| case FUTEX_CMP_REQUEUE_PI: |
| return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); |
| } |
| return -ENOSYS; |
| } |
| |
| |
| SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, |
| struct timespec __user *, utime, u32 __user *, uaddr2, |
| u32, val3) |
| { |
| struct timespec ts; |
| ktime_t t, *tp = NULL; |
| u32 val2 = 0; |
| int cmd = op & FUTEX_CMD_MASK; |
| |
| if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || |
| cmd == FUTEX_WAIT_BITSET || |
| cmd == FUTEX_WAIT_REQUEUE_PI)) { |
| if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) |
| return -EFAULT; |
| if (copy_from_user(&ts, utime, sizeof(ts)) != 0) |
| return -EFAULT; |
| if (!timespec_valid(&ts)) |
| return -EINVAL; |
| |
| t = timespec_to_ktime(ts); |
| if (cmd == FUTEX_WAIT) |
| t = ktime_add_safe(ktime_get(), t); |
| tp = &t; |
| } |
| /* |
| * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. |
| * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. |
| */ |
| if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || |
| cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) |
| val2 = (u32) (unsigned long) utime; |
| |
| return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); |
| } |
| |
| static void __init futex_detect_cmpxchg(void) |
| { |
| #ifndef CONFIG_HAVE_FUTEX_CMPXCHG |
| u32 curval; |
| |
| /* |
| * This will fail and we want it. Some arch implementations do |
| * runtime detection of the futex_atomic_cmpxchg_inatomic() |
| * functionality. We want to know that before we call in any |
| * of the complex code paths. Also we want to prevent |
| * registration of robust lists in that case. NULL is |
| * guaranteed to fault and we get -EFAULT on functional |
| * implementation, the non-functional ones will return |
| * -ENOSYS. |
| */ |
| if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) |
| futex_cmpxchg_enabled = 1; |
| #endif |
| } |
| |
| static int __init futex_init(void) |
| { |
| unsigned int futex_shift; |
| unsigned long i; |
| |
| #if CONFIG_BASE_SMALL |
| futex_hashsize = 16; |
| #else |
| futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); |
| #endif |
| |
| futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), |
| futex_hashsize, 0, |
| futex_hashsize < 256 ? HASH_SMALL : 0, |
| &futex_shift, NULL, |
| futex_hashsize, futex_hashsize); |
| futex_hashsize = 1UL << futex_shift; |
| |
| futex_detect_cmpxchg(); |
| |
| for (i = 0; i < futex_hashsize; i++) { |
| atomic_set(&futex_queues[i].waiters, 0); |
| plist_head_init(&futex_queues[i].chain); |
| spin_lock_init(&futex_queues[i].lock); |
| } |
| |
| return 0; |
| } |
| core_initcall(futex_init); |