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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>
This commit is contained in:
Ben Segall 2013-10-16 11:16:12 -07:00 committed by Ingo Molnar
parent ac9ff7997b
commit 1ee14e6c8c
3 changed files with 19 additions and 9 deletions
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9
kernel/sched/core.c
View File

@ -7436,7 +7436,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
runtime_enabled = quota != RUNTIME_INF; runtime_enabled = quota != RUNTIME_INF;
runtime_was_enabled = cfs_b->quota != RUNTIME_INF; runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
account_cfs_bandwidth_used(runtime_enabled, runtime_was_enabled); /*
* If we need to toggle cfs_bandwidth_used, off->on must occur
* before making related changes, and on->off must occur afterwards
*/
if (runtime_enabled && !runtime_was_enabled)
cfs_bandwidth_usage_inc();
raw_spin_lock_irq(&cfs_b->lock); raw_spin_lock_irq(&cfs_b->lock);
cfs_b->period = ns_to_ktime(period); cfs_b->period = ns_to_ktime(period);
cfs_b->quota = quota; cfs_b->quota = quota;
@ -7462,6 +7467,8 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
unthrottle_cfs_rq(cfs_rq); unthrottle_cfs_rq(cfs_rq);
raw_spin_unlock_irq(&rq->lock); raw_spin_unlock_irq(&rq->lock);
} }
if (runtime_was_enabled && !runtime_enabled)
cfs_bandwidth_usage_dec();
out_unlock: out_unlock:
mutex_unlock(&cfs_constraints_mutex); mutex_unlock(&cfs_constraints_mutex);

16
kernel/sched/fair.c
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@ -2845,13 +2845,14 @@ static inline bool cfs_bandwidth_used(void)
return static_key_false(&__cfs_bandwidth_used); return static_key_false(&__cfs_bandwidth_used);
} }
void account_cfs_bandwidth_used(int enabled, int was_enabled) void cfs_bandwidth_usage_inc(void)
{ {
/* only need to count groups transitioning between enabled/!enabled */ static_key_slow_inc(&__cfs_bandwidth_used);
if (enabled && !was_enabled) }
static_key_slow_inc(&__cfs_bandwidth_used);
else if (!enabled && was_enabled) void cfs_bandwidth_usage_dec(void)
static_key_slow_dec(&__cfs_bandwidth_used); {
static_key_slow_dec(&__cfs_bandwidth_used);
} }
#else /* HAVE_JUMP_LABEL */ #else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void) static bool cfs_bandwidth_used(void)
@ -2859,7 +2860,8 @@ static bool cfs_bandwidth_used(void)
return true; return true;
} }
void account_cfs_bandwidth_used(int enabled, int was_enabled) {} void cfs_bandwidth_usage_inc(void) {}
void cfs_bandwidth_usage_dec(void) {}
#endif /* HAVE_JUMP_LABEL */ #endif /* HAVE_JUMP_LABEL */
/* /*

3
kernel/sched/sched.h
View File

@ -1352,7 +1352,8 @@ extern void print_rt_stats(struct seq_file *m, int cpu);
extern void init_cfs_rq(struct cfs_rq *cfs_rq); extern void init_cfs_rq(struct cfs_rq *cfs_rq);
extern void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq); extern void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq);
extern void account_cfs_bandwidth_used(int enabled, int was_enabled); extern void cfs_bandwidth_usage_inc(void);
extern void cfs_bandwidth_usage_dec(void);
#ifdef CONFIG_NO_HZ_COMMON #ifdef CONFIG_NO_HZ_COMMON
enum rq_nohz_flag_bits { enum rq_nohz_flag_bits {