[S390] fix recursive locking on page_table_lock
Suzuki Poulose reported the following recursive locking bug on s390:
Here is the stack trace : (see Appendix I for more info)
[<0000000000406ed6>] _spin_lock+0x52/0x94
[<0000000000103bde>] crst_table_free+0x14e/0x1a4
[<00000000001ba684>] __pmd_alloc+0x114/0x1ec
[<00000000001be8d0>] handle_mm_fault+0x2cc/0xb80
[<0000000000407d62>] do_dat_exception+0x2b6/0x3a0
[<0000000000114f8c>] sysc_return+0x0/0x8
[<00000200001642b2>] 0x200001642b2
The page_table_lock is already acquired in __pmd_alloc (mm/memory.c) and
it tries to populate the pud/pgd with a new pmd allocated. If another
thread populates it before we get a chance, we free the pmd using
pmd_free().
On s390x, pmd_free(even pud_free ) is #defined to crst_table_free(),
which acquires the page_table_lock to protect the crst_table index updates.
Hence this ends up in a recursive locking of the page_table_lock.
The solution suggested by Dave Hansen is to use a new spin lock in the mmu
context to protect the access to the crst_list and the pgtable_list.
Reported-by: Suzuki Poulose <suzuki@in.ibm.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index 3b59216..03be999 100644
--- a/arch/s390/include/asm/mmu.h
+++ b/arch/s390/include/asm/mmu.h
@@ -2,6 +2,7 @@
#define __MMU_H
typedef struct {
+ spinlock_t list_lock;
struct list_head crst_list;
struct list_head pgtable_list;
unsigned long asce_bits;
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index b2658b9..ddad590 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -140,6 +140,7 @@
static inline pgd_t *pgd_alloc(struct mm_struct *mm)
{
+ spin_lock_init(&mm->context.list_lock);
INIT_LIST_HEAD(&mm->context.crst_list);
INIT_LIST_HEAD(&mm->context.pgtable_list);
return (pgd_t *) crst_table_alloc(mm, s390_noexec);
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 5656672..c702152 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -78,9 +78,9 @@
}
page->index = page_to_phys(shadow);
}
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
list_add(&page->lru, &mm->context.crst_list);
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
return (unsigned long *) page_to_phys(page);
}
@@ -89,9 +89,9 @@
unsigned long *shadow = get_shadow_table(table);
struct page *page = virt_to_page(table);
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
list_del(&page->lru);
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
if (shadow)
free_pages((unsigned long) shadow, ALLOC_ORDER);
free_pages((unsigned long) table, ALLOC_ORDER);
@@ -182,7 +182,7 @@
unsigned long bits;
bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
page = NULL;
if (!list_empty(&mm->context.pgtable_list)) {
page = list_first_entry(&mm->context.pgtable_list,
@@ -191,7 +191,7 @@
page = NULL;
}
if (!page) {
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
if (!page)
return NULL;
@@ -202,7 +202,7 @@
clear_table_pgstes(table);
else
clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
list_add(&page->lru, &mm->context.pgtable_list);
}
table = (unsigned long *) page_to_phys(page);
@@ -213,7 +213,7 @@
page->flags |= bits;
if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
list_move_tail(&page->lru, &mm->context.pgtable_list);
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
return table;
}
@@ -225,7 +225,7 @@
bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
page->flags ^= bits;
if (page->flags & FRAG_MASK) {
/* Page now has some free pgtable fragments. */
@@ -234,7 +234,7 @@
} else
/* All fragments of the 4K page have been freed. */
list_del(&page->lru);
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
if (page) {
pgtable_page_dtor(page);
__free_page(page);
@@ -245,7 +245,7 @@
{
struct page *page;
- spin_lock(&mm->page_table_lock);
+ spin_lock(&mm->context.list_lock);
/* Free shadow region and segment tables. */
list_for_each_entry(page, &mm->context.crst_list, lru)
if (page->index) {
@@ -255,7 +255,7 @@
/* "Free" second halves of page tables. */
list_for_each_entry(page, &mm->context.pgtable_list, lru)
page->flags &= ~SECOND_HALVES;
- spin_unlock(&mm->page_table_lock);
+ spin_unlock(&mm->context.list_lock);
mm->context.noexec = 0;
update_mm(mm, tsk);
}
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index e4868bf..5f91a38 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -331,6 +331,7 @@
unsigned long start, end;
int i;
+ spin_lock_init(&init_mm.context.list_lock);
INIT_LIST_HEAD(&init_mm.context.crst_list);
INIT_LIST_HEAD(&init_mm.context.pgtable_list);
init_mm.context.noexec = 0;