Commit-ID: f235a54f00449c611f85173fe8a66c4d189c5ce1 Gitweb: http://git.kernel.org/tip/f235a54f00449c611f85173fe8a66c4d189c5ce1 Author: Vincent Guittot <vincent.guit...@linaro.org> AuthorDate: Sat, 1 Jul 2017 07:06:13 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 10 Aug 2017 12:18:15 +0200
sched/pelt: Fix false running accounting The running state is a subset of runnable state which means that running can't be set if runnable (weight) is cleared. There are corner cases where the current sched_entity has been already dequeued but cfs_rq->curr has not been updated yet and still points to the dequeued sched_entity. If ___update_load_avg() is called at that time, weight will be 0 and running will be set which is not possible. This case happens during pick_next_task_fair() when a cfs_rq becomes idles. The current sched_entity has been dequeued so se->on_rq is cleared and cfs_rq->weight is null. But cfs_rq->curr still points to se (it will be cleared when picking the idle thread). Because the cfs_rq becomes idle, idle_balance() is called and ends up to call update_blocked_averages() with these wrong running and runnable states. Add a test in ___update_load_avg() to correct the running state in this case. Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: morten.rasmus...@arm.com Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: dietmar.eggem...@arm.com Link: http://lkml.kernel.org/r/1498885573-18984-1-git-send-email-vincent.guit...@linaro.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/sched/fair.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 75c58c7..ef5b66b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2991,6 +2991,18 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa, sa->last_update_time += delta << 10; /* + * running is a subset of runnable (weight) so running can't be set if + * runnable is clear. But there are some corner cases where the current + * se has been already dequeued but cfs_rq->curr still points to it. + * This means that weight will be 0 but not running for a sched_entity + * but also for a cfs_rq if the latter becomes idle. As an example, + * this happens during idle_balance() which calls + * update_blocked_averages() + */ + if (!weight) + running = 0; + + /* * Now we know we crossed measurement unit boundaries. The *_avg * accrues by two steps: *
