@@ -4773,18 +4773,21 @@ again:
* entity, update_curr() will update its vruntime, otherwise
* forget we've ever seen it.
*/
- if (curr && curr->on_rq)
- update_curr(cfs_rq);
- else
- curr = NULL;
+ if (curr) {
+ if (curr->on_rq)
+ update_curr(cfs_rq);
+ else
+ curr = NULL;
- /*
- * This call to check_cfs_rq_runtime() will do the throttle and
- * dequeue its entity in the parent(s). Therefore the 'simple'
- * nr_running test will indeed be correct.
- */
- if (unlikely(check_cfs_rq_runtime(cfs_rq)))
- goto simple;
+ /*
+ * This call to check_cfs_rq_runtime() will do the
+ * throttle and dequeue its entity in the parent(s).
+ * Therefore the 'simple' nr_running test will indeed
+ * be correct.
+ */
+ if (unlikely(check_cfs_rq_runtime(cfs_rq)))
+ goto simple;
+ }
se = pick_next_entity(cfs_rq, curr);
cfs_rq = group_cfs_rq(se);
This is a note to let you know that I have just added a patch titled sched/fair: Prevent throttling in early pick_next_task_fair() to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt15. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From f372a3a214b20a3b194b36dcb7939384cc7425a3 Mon Sep 17 00:00:00 2001 From: Ben Segall <bsegall@google.com> Date: Mon, 6 Apr 2015 15:28:10 -0700 Subject: sched/fair: Prevent throttling in early pick_next_task_fair() commit 54d27365cae88fbcc853b391dcd561e71acb81fa upstream. The optimized task selection logic optimistically selects a new task to run without first doing a full put_prev_task(). This is so that we can avoid a put/set on the common ancestors of the old and new task. Similarly, we should only call check_cfs_rq_runtime() to throttle eligible groups if they're part of the common ancestry, otherwise it is possible to end up with no eligible task in the simple task selection. Imagine: /root /prev /next /A /B If our optimistic selection ends up throttling /next, we goto simple and our put_prev_task() ends up throttling /prev, after which we're going to bug out in set_next_entity() because there aren't any tasks left. Avoid this scenario by only throttling common ancestors. Reported-by: Mohammed Naser <mnaser@vexxhost.com> Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Ben Segall <bsegall@google.com> [ munged Changelog ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Roman Gushchin <klamm@yandex-team.ru> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: pjt@google.com Fixes: 678d5718d8d0 ("sched/fair: Optimize cgroup pick_next_task_fair()") Link: http://lkml.kernel.org/r/xm26wq1oswoq.fsf@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- kernel/sched/fair.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-)