This is a note to let you know that I've just added the patch titled
sched: Fix race on toggling cfs_bandwidth_used
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fix-race-on-toggling-cfs_bandwidth_used.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 1ee14e6c8cddeeb8a490d7b54cd9016e4bb900b4 Mon Sep 17 00:00:00 2001
From: Ben Segall <[email protected]>
Date: Wed, 16 Oct 2013 11:16:12 -0700
Subject: sched: Fix race on toggling cfs_bandwidth_used
From: Ben Segall <[email protected]>
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 <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: [email protected]
Link:
http://lkml.kernel.org/r/20131016181611.22647.80365.st...@sword-of-the-dawn.mtv.corp.google.com
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Chris J Arges <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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 {
Patches currently in stable-queue which might be from [email protected] are
queue-3.12/sched-fix-hrtimer_cancel-rq-lock-deadlock.patch
queue-3.12/sched-fix-cfs_bandwidth-misuse-of-hrtimer_expires_remaining.patch
queue-3.12/sched-fix-race-on-toggling-cfs_bandwidth_used.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
