sched: Avoid throttle_cfs_rq() racing with period_timer stopping
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>
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@ -229,6 +229,14 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
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atomic_read(&cfs_rq->tg->runnable_avg));
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#endif
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#endif
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#ifdef CONFIG_CFS_BANDWIDTH
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SEQ_printf(m, " .%-30s: %d\n", "tg->cfs_bandwidth.timer_active",
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cfs_rq->tg->cfs_bandwidth.timer_active);
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SEQ_printf(m, " .%-30s: %d\n", "throttled",
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cfs_rq->throttled);
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SEQ_printf(m, " .%-30s: %d\n", "throttle_count",
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cfs_rq->throttle_count);
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#endif
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#ifdef CONFIG_FAIR_GROUP_SCHED
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print_cfs_group_stats(m, cpu, cfs_rq->tg);
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@ -3112,6 +3112,8 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
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cfs_rq->throttled_clock = rq_clock(rq);
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raw_spin_lock(&cfs_b->lock);
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list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
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if (!cfs_b->timer_active)
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__start_cfs_bandwidth(cfs_b);
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raw_spin_unlock(&cfs_b->lock);
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}
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