From 094f469172e00d6ab0a3130b0e01c83b3cf3a98d Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 16 Jun 2016 15:57:01 +0300 Subject: [PATCH] sched/fair: Initialize throttle_count for new task-groups lazily Cgroup created inside throttled group must inherit current throttle_count. Broken throttle_count allows to nominate throttled entries as a next buddy, later this leads to null pointer dereference in pick_next_task_fair(). This patch initialize cfs_rq->throttle_count at first enqueue: laziness allows to skip locking all rq at group creation. Lazy approach also allows to skip full sub-tree scan at throttling hierarchy (not in this patch). Signed-off-by: Konstantin Khlebnikov Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: bsegall@google.com Link: http://lkml.kernel.org/r/146608182119.21870.8439834428248129633.stgit@buzz Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 20 ++++++++++++++++++++ kernel/sched/sched.h | 2 +- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2ae68f0e3bf5..8c5d8c0c8827 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4202,6 +4202,26 @@ static void check_enqueue_throttle(struct cfs_rq *cfs_rq) if (!cfs_bandwidth_used()) return; + /* Synchronize hierarchical throttle counter: */ + if (unlikely(!cfs_rq->throttle_uptodate)) { + struct rq *rq = rq_of(cfs_rq); + struct cfs_rq *pcfs_rq; + struct task_group *tg; + + cfs_rq->throttle_uptodate = 1; + + /* Get closest up-to-date node, because leaves go first: */ + for (tg = cfs_rq->tg->parent; tg; tg = tg->parent) { + pcfs_rq = tg->cfs_rq[cpu_of(rq)]; + if (pcfs_rq->throttle_uptodate) + break; + } + if (tg) { + cfs_rq->throttle_count = pcfs_rq->throttle_count; + cfs_rq->throttled_clock_task = rq_clock_task(rq); + } + } + /* an active group must be handled by the update_curr()->put() path */ if (!cfs_rq->runtime_enabled || cfs_rq->curr) return; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 72f1f3087b04..7cbeb92a1cb9 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -437,7 +437,7 @@ struct cfs_rq { u64 throttled_clock, throttled_clock_task; u64 throttled_clock_task_time; - int throttled, throttle_count; + int throttled, throttle_count, throttle_uptodate; struct list_head throttled_list; #endif /* CONFIG_CFS_BANDWIDTH */ #endif /* CONFIG_FAIR_GROUP_SCHED */