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authorRoman Gushchin <klamm@yandex-team.ru>2014-05-19 15:10:09 +0400
committerIngo Molnar <mingo@kernel.org>2014-06-05 11:51:34 +0200
commit09dc4ab03936df5c5aa711d27c81283c6d09f495 (patch)
tree58266dad582dcf05a46036b2a75a5b9de57872ca
parent0f397f2c90ce68821ee864c2c53baafe78de765d (diff)
downloadop-kernel-dev-09dc4ab03936df5c5aa711d27c81283c6d09f495.zip
op-kernel-dev-09dc4ab03936df5c5aa711d27c81283c6d09f495.tar.gz
sched/fair: Fix tg_set_cfs_bandwidth() deadlock on rq->lock
tg_set_cfs_bandwidth() sets cfs_b->timer_active to 0 to force the period timer restart. It's not safe, because can lead to deadlock, described in commit 927b54fccbf0: "__start_cfs_bandwidth calls hrtimer_cancel while holding rq->lock, waiting for the hrtimer to finish. However, if sched_cfs_period_timer runs for another loop iteration, the hrtimer can attempt to take rq->lock, resulting in deadlock." Three CPUs must be involved: CPU0 CPU1 CPU2 take rq->lock period timer fired ... take cfs_b lock ... ... tg_set_cfs_bandwidth() throttle_cfs_rq() release cfs_b lock take cfs_b lock ... distribute_cfs_runtime() timer_active = 0 take cfs_b->lock wait for rq->lock ... __start_cfs_bandwidth() {wait for timer callback break if timer_active == 1} So, CPU0 and CPU1 are deadlocked. Instead of resetting cfs_b->timer_active, tg_set_cfs_bandwidth can wait for period timer callbacks (ignoring cfs_b->timer_active) and restart the timer explicitly. Signed-off-by: Roman Gushchin <klamm@yandex-team.ru> Reviewed-by: Ben Segall <bsegall@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/87wqdi9g8e.wl\%klamm@yandex-team.ru Cc: pjt@google.com Cc: chris.j.arges@canonical.com Cc: gregkh@linuxfoundation.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/sched/core.c3
-rw-r--r--kernel/sched/fair.c8
-rw-r--r--kernel/sched/sched.h2
3 files changed, 6 insertions, 7 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 540542b..f3f48e7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7751,8 +7751,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
/* restart the period timer (if active) to handle new period expiry */
if (runtime_enabled && cfs_b->timer_active) {
/* force a reprogram */
- cfs_b->timer_active = 0;
- __start_cfs_bandwidth(cfs_b);
+ __start_cfs_bandwidth(cfs_b, true);
}
raw_spin_unlock_irq(&cfs_b->lock);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b4768c0..8cbe2d2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3130,7 +3130,7 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
*/
if (!cfs_b->timer_active) {
__refill_cfs_bandwidth_runtime(cfs_b);
- __start_cfs_bandwidth(cfs_b);
+ __start_cfs_bandwidth(cfs_b, false);
}
if (cfs_b->runtime > 0) {
@@ -3309,7 +3309,7 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
raw_spin_lock(&cfs_b->lock);
list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
if (!cfs_b->timer_active)
- __start_cfs_bandwidth(cfs_b);
+ __start_cfs_bandwidth(cfs_b, false);
raw_spin_unlock(&cfs_b->lock);
}
@@ -3691,7 +3691,7 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
}
/* requires cfs_b->lock, may release to reprogram timer */
-void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
+void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b, bool force)
{
/*
* The timer may be active because we're trying to set a new bandwidth
@@ -3706,7 +3706,7 @@ void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
cpu_relax();
raw_spin_lock(&cfs_b->lock);
/* if someone else restarted the timer then we're done */
- if (cfs_b->timer_active)
+ if (!force && cfs_b->timer_active)
return;
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 456e492..369b4d6 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -278,7 +278,7 @@ extern void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b);
extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
extern void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b);
-extern void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b);
+extern void __start_cfs_bandwidth(struct cfs_bandwidth *cfs_b, bool force);
extern void unthrottle_cfs_rq(struct cfs_rq *cfs_rq);
extern void free_rt_sched_group(struct task_group *tg);
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