diff options
authorBen Segall <bsegall@google.com>2013-10-16 11:16:32 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-01-08 09:42:12 -0800
commitdfb473b35096a0ffae221c7eeb49c34882ea6f9c (patch)
parent05bbcdd32afbfd520c71ae8104a8bf531aed9163 (diff)
sched: Avoid throttle_cfs_rq() racing with period_timer stopping
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@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Chris J Arges <chris.j.arges@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2 files changed, 10 insertions, 0 deletions
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 09acaa15161d..2f9ac8ff1e80 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -215,6 +215,14 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
SEQ_printf(m, " .%-30s: %d\n", "load_tg",
+ 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);
print_cfs_group_stats(m, cpu, cfs_rq->tg);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 33c8b6038002..efe9253bd235 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1655,6 +1655,8 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
cfs_rq->throttled_timestamp = rq->clock;
list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
+ if (!cfs_b->timer_active)
+ __start_cfs_bandwidth(cfs_b);