sched: Fix race on toggling cfs_bandwidth_used
When we transition cfs_bandwidth_used to false, any currently throttled groups will incorrectly return false from cfs_rq_throttled. While tg_set_cfs_bandwidth will unthrottle them eventually, currently running code (including at least dequeue_task_fair and distribute_cfs_runtime) will cause errors. Fix this by turning off cfs_bandwidth_used only after unthrottling all cfs_rqs. Tested: toggle bandwidth back and forth on a loaded cgroup. Caused crashes in minutes without the patch, hasn't crashed with it. 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/20131016181611.22647.80365.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -7436,7 +7436,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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runtime_enabled = quota != RUNTIME_INF;
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runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
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account_cfs_bandwidth_used(runtime_enabled, runtime_was_enabled);
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/*
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* If we need to toggle cfs_bandwidth_used, off->on must occur
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* before making related changes, and on->off must occur afterwards
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*/
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if (runtime_enabled && !runtime_was_enabled)
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cfs_bandwidth_usage_inc();
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raw_spin_lock_irq(&cfs_b->lock);
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cfs_b->period = ns_to_ktime(period);
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cfs_b->quota = quota;
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@ -7462,6 +7467,8 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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unthrottle_cfs_rq(cfs_rq);
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raw_spin_unlock_irq(&rq->lock);
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}
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if (runtime_was_enabled && !runtime_enabled)
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cfs_bandwidth_usage_dec();
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out_unlock:
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mutex_unlock(&cfs_constraints_mutex);
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@ -2845,12 +2845,13 @@ static inline bool cfs_bandwidth_used(void)
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return static_key_false(&__cfs_bandwidth_used);
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}
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void account_cfs_bandwidth_used(int enabled, int was_enabled)
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void cfs_bandwidth_usage_inc(void)
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{
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/* only need to count groups transitioning between enabled/!enabled */
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if (enabled && !was_enabled)
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static_key_slow_inc(&__cfs_bandwidth_used);
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else if (!enabled && was_enabled)
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}
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void cfs_bandwidth_usage_dec(void)
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{
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static_key_slow_dec(&__cfs_bandwidth_used);
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}
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#else /* HAVE_JUMP_LABEL */
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@ -2859,7 +2860,8 @@ static bool cfs_bandwidth_used(void)
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return true;
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}
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void account_cfs_bandwidth_used(int enabled, int was_enabled) {}
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void cfs_bandwidth_usage_inc(void) {}
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void cfs_bandwidth_usage_dec(void) {}
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#endif /* HAVE_JUMP_LABEL */
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/*
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@ -1352,7 +1352,8 @@ extern void print_rt_stats(struct seq_file *m, int cpu);
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extern void init_cfs_rq(struct cfs_rq *cfs_rq);
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extern void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq);
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extern void account_cfs_bandwidth_used(int enabled, int was_enabled);
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extern void cfs_bandwidth_usage_inc(void);
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extern void cfs_bandwidth_usage_dec(void);
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#ifdef CONFIG_NO_HZ_COMMON
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enum rq_nohz_flag_bits {
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