This is a note to let you know that I've just added the patch titled
sched: Avoid throttle_cfs_rq() racing with period_timer stopping
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-avoid-throttle_cfs_rq-racing-with-period_timer-stopping.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f9f9ffc237dd924f048204e8799da74f9ecf40cf Mon Sep 17 00:00:00 2001
From: Ben Segall <bsegall@xxxxxxxxxx>
Date: Wed, 16 Oct 2013 11:16:32 -0700
Subject: sched: Avoid throttle_cfs_rq() racing with period_timer stopping
From: Ben Segall <bsegall@xxxxxxxxxx>
commit f9f9ffc237dd924f048204e8799da74f9ecf40cf upstream.
throttle_cfs_rq() doesn't check to make sure that period_timer is running,
and while update_curr/assign_cfs_runtime does, a concurrently running
period_timer on another cpu could cancel itself between this cpu's
update_curr and throttle_cfs_rq(). If there are no other cfs_rqs running
in the tg to restart the timer, this causes the cfs_rq to be stranded
forever.
Fix this by calling __start_cfs_bandwidth() in throttle if the timer is
inactive.
(Also add some sched_debug lines for cfs_bandwidth.)
Tested: make a run/sleep task in a cgroup, loop switching the cgroup
between 1ms/100ms quota and unlimited, checking for timer_active=0 and
throttled=1 as a failure. With the throttle_cfs_rq() change commented out
this fails, with the full patch it passes.
Signed-off-by: Ben Segall <bsegall@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: pjt@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/debug.c | 8 ++++++++
kernel/sched/fair.c | 2 ++
2 files changed, 10 insertions(+)
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -225,6 +225,14 @@ void print_cfs_rq(struct seq_file *m, in
atomic_read(&cfs_rq->tg->runnable_avg));
#endif
#endif
+#ifdef CONFIG_CFS_BANDWIDTH
+ SEQ_printf(m, " .%-30s: %d\n", "tg->cfs_bandwidth.timer_active",
+ cfs_rq->tg->cfs_bandwidth.timer_active);
+ SEQ_printf(m, " .%-30s: %d\n", "throttled",
+ cfs_rq->throttled);
+ SEQ_printf(m, " .%-30s: %d\n", "throttle_count",
+ cfs_rq->throttle_count);
+#endif
#ifdef CONFIG_FAIR_GROUP_SCHED
print_cfs_group_stats(m, cpu, cfs_rq->tg);
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2335,6 +2335,8 @@ static void throttle_cfs_rq(struct cfs_r
cfs_rq->throttled_clock = rq_clock(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);
raw_spin_unlock(&cfs_b->lock);
}
Patches currently in stable-queue which might be from bsegall@xxxxxxxxxx are
queue-3.12/sched-avoid-throttle_cfs_rq-racing-with-period_timer-stopping.patch
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