From: Paul Turner Date: Thu, 21 Jul 2011 16:43:37 +0000 (-0700) Subject: sched: Prevent buddy interactions with throttled entities X-Git-Tag: upstream/snapshot3+hdmi~8921^2~26 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=5238cdd3873e67a98b28c1161d65d2a615c320a3;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git sched: Prevent buddy interactions with throttled entities Buddies allow us to select "on-rq" entities without actually selecting them from a cfs_rq's rb_tree. As a result we must ensure that throttled entities are not falsely nominated as buddies. The fact that entities are dequeued within throttle_entity is not sufficient for clearing buddy status as the nomination may occur after throttling. Signed-off-by: Paul Turner Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20110721184757.886850167@google.com Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 5a20894..1d4acbe 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -2348,6 +2348,15 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ if (unlikely(se == pse)) return; + /* + * This is possible from callers such as pull_task(), in which we + * unconditionally check_prempt_curr() after an enqueue (which may have + * lead to a throttle). This both saves work and prevents false + * next-buddy nomination below. + */ + if (unlikely(throttled_hierarchy(cfs_rq_of(pse)))) + return; + if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) { set_next_buddy(pse); next_buddy_marked = 1; @@ -2356,6 +2365,12 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_ /* * We can come here with TIF_NEED_RESCHED already set from new task * wake up path. + * + * Note: this also catches the edge-case of curr being in a throttled + * group (e.g. via set_curr_task), since update_curr() (in the + * enqueue of curr) will have resulted in resched being set. This + * prevents us from potentially nominating it as a false LAST_BUDDY + * below. */ if (test_tsk_need_resched(curr)) return; @@ -2474,7 +2489,8 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp { struct sched_entity *se = &p->se; - if (!se->on_rq) + /* throttled hierarchies are not runnable */ + if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se))) return false; /* Tell the scheduler that we'd really like pse to run next. */