timers: fix itimer/many thread hang, v2
This is the second resubmission of the posix timer rework patch, posted
a few days ago.
This includes the changes from the previous resubmittion, which addressed
Oleg Nesterov's comments, removing the RCU stuff from the patch and
un-inlining the thread_group_cputime() function for SMP.
In addition, per Ingo Molnar it simplifies the UP code, consolidating much
of it with the SMP version and depending on lower-level SMP/UP handling to
take care of the differences.
It also cleans up some UP compile errors, moves the scheduler stats-related
macros into kernel/sched_stats.h, cleans up a merge error in
kernel/fork.c and has a few other minor fixes and cleanups as suggested
by Oleg and Ingo. Thanks for the review, guys.
Signed-off-by: Frank Mayhar <fmayhar@google.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/fork.c b/kernel/fork.c
index 1181b9a..021ae01 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -791,7 +791,7 @@
int ret;
if (clone_flags & CLONE_THREAD) {
- ret = thread_group_cputime_clone_thread(current, tsk);
+ ret = thread_group_cputime_clone_thread(current);
if (likely(!ret)) {
atomic_inc(¤t->signal->count);
atomic_inc(¤t->signal->live);
@@ -834,9 +834,6 @@
sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
task_io_accounting_init(&sig->ioac);
- INIT_LIST_HEAD(&sig->cpu_timers[0]);
- INIT_LIST_HEAD(&sig->cpu_timers[1]);
- INIT_LIST_HEAD(&sig->cpu_timers[2]);
taskstats_tgid_init(sig);
task_lock(current->group_leader);
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 9a7ea04..153dcb2 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -7,50 +7,46 @@
#include <linux/errno.h>
#include <linux/math64.h>
#include <asm/uaccess.h>
+#include <linux/kernel_stat.h>
-#ifdef CONFIG_SMP
/*
- * Allocate the thread_group_cputime structure appropriately for SMP kernels
- * and fill in the current values of the fields. Called from copy_signal()
- * via thread_group_cputime_clone_thread() when adding a second or subsequent
+ * Allocate the thread_group_cputime structure appropriately and fill in the
+ * current values of the fields. Called from copy_signal() via
+ * thread_group_cputime_clone_thread() when adding a second or subsequent
* thread to a thread group. Assumes interrupts are enabled when called.
*/
-int thread_group_cputime_alloc_smp(struct task_struct *tsk)
+int thread_group_cputime_alloc(struct task_struct *tsk)
{
struct signal_struct *sig = tsk->signal;
struct task_cputime *cputime;
/*
* If we have multiple threads and we don't already have a
- * per-CPU task_cputime struct, allocate one and fill it in with
- * the times accumulated so far.
+ * per-CPU task_cputime struct (checked in the caller), allocate
+ * one and fill it in with the times accumulated so far. We may
+ * race with another thread so recheck after we pick up the sighand
+ * lock.
*/
- if (sig->cputime.totals)
- return 0;
cputime = alloc_percpu(struct task_cputime);
if (cputime == NULL)
return -ENOMEM;
- read_lock(&tasklist_lock);
spin_lock_irq(&tsk->sighand->siglock);
if (sig->cputime.totals) {
spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
free_percpu(cputime);
return 0;
}
sig->cputime.totals = cputime;
- cputime = per_cpu_ptr(sig->cputime.totals, get_cpu());
+ cputime = per_cpu_ptr(sig->cputime.totals, smp_processor_id());
cputime->utime = tsk->utime;
cputime->stime = tsk->stime;
cputime->sum_exec_runtime = tsk->se.sum_exec_runtime;
- put_cpu_no_resched();
spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
return 0;
}
/**
- * thread_group_cputime_smp - Sum the thread group time fields across all CPUs.
+ * thread_group_cputime - Sum the thread group time fields across all CPUs.
*
* @tsk: The task we use to identify the thread group.
* @times: task_cputime structure in which we return the summed fields.
@@ -58,7 +54,7 @@
* Walk the list of CPUs to sum the per-CPU time fields in the thread group
* time structure.
*/
-void thread_group_cputime_smp(
+void thread_group_cputime(
struct task_struct *tsk,
struct task_cputime *times)
{
@@ -83,8 +79,6 @@
}
}
-#endif /* CONFIG_SMP */
-
/*
* Called after updating RLIMIT_CPU to set timer expiration if necessary.
*/
@@ -300,35 +294,7 @@
cpu->cpu = virt_ticks(p);
break;
case CPUCLOCK_SCHED:
- cpu->sched = task_sched_runtime(p);
- break;
- }
- return 0;
-}
-
-/*
- * Sample a process (thread group) clock for the given group_leader task.
- * Must be called with tasklist_lock held for reading.
- * Must be called with tasklist_lock held for reading, and p->sighand->siglock.
- */
-static int cpu_clock_sample_group_locked(unsigned int clock_idx,
- struct task_struct *p,
- union cpu_time_count *cpu)
-{
- struct task_cputime cputime;
-
- thread_group_cputime(p, &cputime);
- switch (clock_idx) {
- default:
- return -EINVAL;
- case CPUCLOCK_PROF:
- cpu->cpu = cputime_add(cputime.utime, cputime.stime);
- break;
- case CPUCLOCK_VIRT:
- cpu->cpu = cputime.utime;
- break;
- case CPUCLOCK_SCHED:
- cpu->sched = thread_group_sched_runtime(p);
+ cpu->sched = p->se.sum_exec_runtime + task_delta_exec(p);
break;
}
return 0;
@@ -342,13 +308,23 @@
struct task_struct *p,
union cpu_time_count *cpu)
{
- int ret;
- unsigned long flags;
- spin_lock_irqsave(&p->sighand->siglock, flags);
- ret = cpu_clock_sample_group_locked(CPUCLOCK_WHICH(which_clock), p,
- cpu);
- spin_unlock_irqrestore(&p->sighand->siglock, flags);
- return ret;
+ struct task_cputime cputime;
+
+ thread_group_cputime(p, &cputime);
+ switch (which_clock) {
+ default:
+ return -EINVAL;
+ case CPUCLOCK_PROF:
+ cpu->cpu = cputime_add(cputime.utime, cputime.stime);
+ break;
+ case CPUCLOCK_VIRT:
+ cpu->cpu = cputime.utime;
+ break;
+ case CPUCLOCK_SCHED:
+ cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
+ break;
+ }
+ return 0;
}
@@ -1324,29 +1300,37 @@
* fastpath_timer_check - POSIX CPU timers fast path.
*
* @tsk: The task (thread) being checked.
- * @sig: The signal pointer for that task.
*
- * If there are no timers set return false. Otherwise snapshot the task and
- * thread group timers, then compare them with the corresponding expiration
- # times. Returns true if a timer has expired, else returns false.
+ * Check the task and thread group timers. If both are zero (there are no
+ * timers set) return false. Otherwise snapshot the task and thread group
+ * timers and compare them with the corresponding expiration times. Return
+ * true if a timer has expired, else return false.
*/
-static inline int fastpath_timer_check(struct task_struct *tsk,
- struct signal_struct *sig)
+static inline int fastpath_timer_check(struct task_struct *tsk)
{
- struct task_cputime task_sample = {
- .utime = tsk->utime,
- .stime = tsk->stime,
- .sum_exec_runtime = tsk->se.sum_exec_runtime
- };
- struct task_cputime group_sample;
+ struct signal_struct *sig = tsk->signal;
- if (task_cputime_zero(&tsk->cputime_expires) &&
- task_cputime_zero(&sig->cputime_expires))
+ if (unlikely(!sig))
return 0;
- if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
- return 1;
- thread_group_cputime(tsk, &group_sample);
- return task_cputime_expired(&group_sample, &sig->cputime_expires);
+
+ if (!task_cputime_zero(&tsk->cputime_expires)) {
+ struct task_cputime task_sample = {
+ .utime = tsk->utime,
+ .stime = tsk->stime,
+ .sum_exec_runtime = tsk->se.sum_exec_runtime
+ };
+
+ if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
+ return 1;
+ }
+ if (!task_cputime_zero(&sig->cputime_expires)) {
+ struct task_cputime group_sample;
+
+ thread_group_cputime(tsk, &group_sample);
+ if (task_cputime_expired(&group_sample, &sig->cputime_expires))
+ return 1;
+ }
+ return 0;
}
/*
@@ -1358,43 +1342,34 @@
{
LIST_HEAD(firing);
struct k_itimer *timer, *next;
- struct signal_struct *sig;
- struct sighand_struct *sighand;
- unsigned long flags;
BUG_ON(!irqs_disabled());
- /* Pick up tsk->signal and make sure it's valid. */
- sig = tsk->signal;
/*
* The fast path checks that there are no expired thread or thread
- * group timers. If that's so, just return. Also check that
- * tsk->signal is non-NULL; this probably can't happen but cover the
- * possibility anyway.
+ * group timers. If that's so, just return.
*/
- if (unlikely(!sig) || !fastpath_timer_check(tsk, sig))
+ if (!fastpath_timer_check(tsk))
return;
- sighand = lock_task_sighand(tsk, &flags);
- if (likely(sighand)) {
- /*
- * Here we take off tsk->signal->cpu_timers[N] and
- * tsk->cpu_timers[N] all the timers that are firing, and
- * put them on the firing list.
- */
- check_thread_timers(tsk, &firing);
- check_process_timers(tsk, &firing);
+ spin_lock(&tsk->sighand->siglock);
+ /*
+ * Here we take off tsk->signal->cpu_timers[N] and
+ * tsk->cpu_timers[N] all the timers that are firing, and
+ * put them on the firing list.
+ */
+ check_thread_timers(tsk, &firing);
+ check_process_timers(tsk, &firing);
- /*
- * We must release these locks before taking any timer's lock.
- * There is a potential race with timer deletion here, as the
- * siglock now protects our private firing list. We have set
- * the firing flag in each timer, so that a deletion attempt
- * that gets the timer lock before we do will give it up and
- * spin until we've taken care of that timer below.
- */
- }
- unlock_task_sighand(tsk, &flags);
+ /*
+ * We must release these locks before taking any timer's lock.
+ * There is a potential race with timer deletion here, as the
+ * siglock now protects our private firing list. We have set
+ * the firing flag in each timer, so that a deletion attempt
+ * that gets the timer lock before we do will give it up and
+ * spin until we've taken care of that timer below.
+ */
+ spin_unlock(&tsk->sighand->siglock);
/*
* Now that all the timers on our list have the firing flag,
@@ -1433,7 +1408,7 @@
struct list_head *head;
BUG_ON(clock_idx == CPUCLOCK_SCHED);
- cpu_clock_sample_group_locked(clock_idx, tsk, &now);
+ cpu_clock_sample_group(clock_idx, tsk, &now);
if (oldval) {
if (!cputime_eq(*oldval, cputime_zero)) {
diff --git a/kernel/sched.c b/kernel/sched.c
index c51b5d2..260c22c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4039,55 +4039,22 @@
/*
* Return any ns on the sched_clock that have not yet been banked in
* @p in case that task is currently running.
- *
- * Called with task_rq_lock() held on @rq.
*/
-static unsigned long long task_delta_exec(struct task_struct *p, struct rq *rq)
+unsigned long long task_delta_exec(struct task_struct *p)
{
+ struct rq *rq;
+ unsigned long flags;
+ u64 ns = 0;
+
+ rq = task_rq_lock(p, &flags);
if (task_current(rq, p)) {
u64 delta_exec;
update_rq_clock(rq);
delta_exec = rq->clock - p->se.exec_start;
if ((s64)delta_exec > 0)
- return delta_exec;
+ ns = delta_exec;
}
- return 0;
-}
-
-/*
- * Return p->sum_exec_runtime plus any more ns on the sched_clock
- * that have not yet been banked in case the task is currently running.
- */
-unsigned long long task_sched_runtime(struct task_struct *p)
-{
- unsigned long flags;
- u64 ns;
- struct rq *rq;
-
- rq = task_rq_lock(p, &flags);
- ns = p->se.sum_exec_runtime + task_delta_exec(p, rq);
- task_rq_unlock(rq, &flags);
-
- return ns;
-}
-
-/*
- * Return sum_exec_runtime for the thread group plus any more ns on the
- * sched_clock that have not yet been banked in case the task is currently
- * running.
- */
-unsigned long long thread_group_sched_runtime(struct task_struct *p)
-{
- unsigned long flags;
- u64 ns;
- struct rq *rq;
- struct task_cputime totals;
-
- rq = task_rq_lock(p, &flags);
- thread_group_cputime(p, &totals);
- ns = totals.sum_exec_runtime + task_delta_exec(p, rq);
- task_rq_unlock(rq, &flags);
return ns;
}
diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 8385d43..d6903bd 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -270,3 +270,139 @@
#define sched_info_switch(t, next) do { } while (0)
#endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */
+/*
+ * The following are functions that support scheduler-internal time accounting.
+ * These functions are generally called at the timer tick. None of this depends
+ * on CONFIG_SCHEDSTATS.
+ */
+
+#ifdef CONFIG_SMP
+
+/**
+ * thread_group_cputime_account_user - Maintain utime for a thread group.
+ *
+ * @tgtimes: Pointer to thread_group_cputime structure.
+ * @cputime: Time value by which to increment the utime field of that
+ * structure.
+ *
+ * If thread group time is being maintained, get the structure for the
+ * running CPU and update the utime field there.
+ */
+static inline void thread_group_cputime_account_user(
+ struct thread_group_cputime *tgtimes,
+ cputime_t cputime)
+{
+ if (tgtimes->totals) {
+ struct task_cputime *times;
+
+ times = per_cpu_ptr(tgtimes->totals, get_cpu());
+ times->utime = cputime_add(times->utime, cputime);
+ put_cpu_no_resched();
+ }
+}
+
+/**
+ * thread_group_cputime_account_system - Maintain stime for a thread group.
+ *
+ * @tgtimes: Pointer to thread_group_cputime structure.
+ * @cputime: Time value by which to increment the stime field of that
+ * structure.
+ *
+ * If thread group time is being maintained, get the structure for the
+ * running CPU and update the stime field there.
+ */
+static inline void thread_group_cputime_account_system(
+ struct thread_group_cputime *tgtimes,
+ cputime_t cputime)
+{
+ if (tgtimes->totals) {
+ struct task_cputime *times;
+
+ times = per_cpu_ptr(tgtimes->totals, get_cpu());
+ times->stime = cputime_add(times->stime, cputime);
+ put_cpu_no_resched();
+ }
+}
+
+/**
+ * thread_group_cputime_account_exec_runtime - Maintain exec runtime for a
+ * thread group.
+ *
+ * @tgtimes: Pointer to thread_group_cputime structure.
+ * @ns: Time value by which to increment the sum_exec_runtime field
+ * of that structure.
+ *
+ * If thread group time is being maintained, get the structure for the
+ * running CPU and update the sum_exec_runtime field there.
+ */
+static inline void thread_group_cputime_account_exec_runtime(
+ struct thread_group_cputime *tgtimes,
+ unsigned long long ns)
+{
+ if (tgtimes->totals) {
+ struct task_cputime *times;
+
+ times = per_cpu_ptr(tgtimes->totals, get_cpu());
+ times->sum_exec_runtime += ns;
+ put_cpu_no_resched();
+ }
+}
+
+#else /* CONFIG_SMP */
+
+static inline void thread_group_cputime_account_user(
+ struct thread_group_cputime *tgtimes,
+ cputime_t cputime)
+{
+ tgtimes->totals->utime = cputime_add(tgtimes->totals->utime, cputime);
+}
+
+static inline void thread_group_cputime_account_system(
+ struct thread_group_cputime *tgtimes,
+ cputime_t cputime)
+{
+ tgtimes->totals->stime = cputime_add(tgtimes->totals->stime, cputime);
+}
+
+static inline void thread_group_cputime_account_exec_runtime(
+ struct thread_group_cputime *tgtimes,
+ unsigned long long ns)
+{
+ tgtimes->totals->sum_exec_runtime += ns;
+}
+
+#endif /* CONFIG_SMP */
+
+/*
+ * These are the generic time-accounting routines that use the above
+ * functions. They are the functions actually called by the scheduler.
+ */
+static inline void account_group_user_time(struct task_struct *tsk,
+ cputime_t cputime)
+{
+ struct signal_struct *sig;
+
+ sig = tsk->signal;
+ if (likely(sig))
+ thread_group_cputime_account_user(&sig->cputime, cputime);
+}
+
+static inline void account_group_system_time(struct task_struct *tsk,
+ cputime_t cputime)
+{
+ struct signal_struct *sig;
+
+ sig = tsk->signal;
+ if (likely(sig))
+ thread_group_cputime_account_system(&sig->cputime, cputime);
+}
+
+static inline void account_group_exec_runtime(struct task_struct *tsk,
+ unsigned long long ns)
+{
+ struct signal_struct *sig;
+
+ sig = tsk->signal;
+ if (likely(sig))
+ thread_group_cputime_account_exec_runtime(&sig->cputime, ns);
+}