[PATCH 3.12 74/77] sched: Fix race on toggling cfs_bandwidth_used
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2014-01-14 00:29:29
Also in:
lkml
3.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ben Segall <bsegall@google.com> 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 <redacted> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- kernel/sched/core.c | 9 ++++++++- kernel/sched/fair.c | 16 +++++++++------- kernel/sched/sched.h | 3 ++- 3 files changed, 19 insertions(+), 9 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c@@ -7277,7 +7277,12 @@ static int tg_set_cfs_bandwidth(struct t 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;
@@ -7303,6 +7308,8 @@ static int tg_set_cfs_bandwidth(struct t 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); --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c
@@ -2077,13 +2077,14 @@ static inline bool cfs_bandwidth_used(vo 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)
@@ -2091,7 +2092,8 @@ 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 */ /* --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h
@@ -1305,7 +1305,8 @@ extern void print_rt_stats(struct seq_fi 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 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 enum rq_nohz_flag_bits {