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author | Roman Gushchin <klamm@yandex-team.ru> | 2014-05-19 13:10:09 +0200 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2014-06-05 11:51:34 +0200 |
commit | 09dc4ab03936df5c5aa711d27c81283c6d09f495 (patch) | |
tree | 58266dad582dcf05a46036b2a75a5b9de57872ca /kernel/sched/sched.h | |
parent | sched/dl: Fix race in dl_task_timer() (diff) | |
download | linux-09dc4ab03936df5c5aa711d27c81283c6d09f495.tar.xz linux-09dc4ab03936df5c5aa711d27c81283c6d09f495.zip |
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>
Diffstat (limited to 'kernel/sched/sched.h')
-rw-r--r-- | kernel/sched/sched.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 456e492a3dca..369b4d663c42 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); |