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| author | Ben Segall <bsegall@google.com> | 2013-10-16 11:16:12 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-01-15 15:27:11 -0800 |
| commit | 16e7480c23d33d9475d45be92c1ddf218575a647 (patch) | |
| tree | 7cf3d25a05f42f95407ab5ea844d88ce451164ec | |
| parent | a63f31f1f2cdb459b121f644ccbd07ae84f45d4e (diff) | |
| download | lwn-16e7480c23d33d9475d45be92c1ddf218575a647.tar.gz lwn-16e7480c23d33d9475d45be92c1ddf218575a647.zip | |
sched: Fix race on toggling cfs_bandwidth_used
commit 1ee14e6c8cddeeb8a490d7b54cd9016e4bb900b4 upstream.
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>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/sched/core.c | 9 | ||||
| -rw-r--r-- | kernel/sched/fair.c | 16 | ||||
| -rw-r--r-- | kernel/sched/sched.h | 3 |
3 files changed, 19 insertions, 9 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4b6c546774b2..3a5b31796edf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7906,7 +7906,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) runtime_enabled = 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); cfs_b->period = ns_to_ktime(period); cfs_b->quota = quota; @@ -7932,6 +7937,8 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) unthrottle_cfs_rq(cfs_rq); raw_spin_unlock_irq(&rq->lock); } + if (runtime_was_enabled && !runtime_enabled) + cfs_bandwidth_usage_dec(); out_unlock: mutex_unlock(&cfs_constraints_mutex); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index efe9253bd235..1eba2640569d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1393,13 +1393,14 @@ static inline bool cfs_bandwidth_used(void) 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 */ - if (enabled && !was_enabled) - static_key_slow_inc(&__cfs_bandwidth_used); - else if (!enabled && was_enabled) - static_key_slow_dec(&__cfs_bandwidth_used); + static_key_slow_inc(&__cfs_bandwidth_used); +} + +void cfs_bandwidth_usage_dec(void) +{ + static_key_slow_dec(&__cfs_bandwidth_used); } #else /* HAVE_JUMP_LABEL */ static bool cfs_bandwidth_used(void) @@ -1407,7 +1408,8 @@ static bool cfs_bandwidth_used(void) 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 */ /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index acfa7017eb0a..4e2bd6c32da7 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1140,7 +1140,8 @@ 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 unthrottle_offline_cfs_rqs(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 enum rq_nohz_flag_bits { |