From c47b2a69f2a1f9ab2c7eb6608ce316891d5cdc19 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 24 Sep 2020 13:50:42 +0200 Subject: [PATCH] sched: Fix rq->nr_iowait ordering schedule() ttwu() deactivate_task(); if (p->on_rq && ...) // false atomic_dec(&task_rq(p)->nr_iowait); if (prev->in_iowait) atomic_inc(&rq->nr_iowait); Allows nr_iowait to be decremented before it gets incremented, resulting in more dodgy IO-wait numbers than usual. Note that because we can now do ttwu_queue_wakelist() before p->on_cpu==0, we lose the natural ordering and have to further delay the decrement. Fixes: c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu") Reported-by: Tejun Heo Signed-off-by: Peter Zijlstra (Intel) Acked-by: Mel Gorman Link: https://lkml.kernel.org/r/20201117093829.GD3121429@hirez.programming.kicks-ass.net Change-Id: Iee2ed007cbdbe9cb1ca8e028d928d263d85e1f2b Signed-off-by: Alexander Winkowski --- kernel/sched/core.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 57a2a3119266..141479ce13e5 100755 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1798,7 +1798,12 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags, #ifdef CONFIG_SMP if (wake_flags & WF_MIGRATED) en_flags |= ENQUEUE_MIGRATED; + else #endif + if (p->in_iowait) { + delayacct_blkio_end(p); + atomic_dec(&task_rq(p)->nr_iowait); + } ttwu_activate(rq, p, en_flags); ttwu_do_wakeup(rq, p, wake_flags, rf); @@ -2215,11 +2220,6 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags, if (READ_ONCE(p->on_rq) && ttwu_remote(p, wake_flags)) goto unlock; - if (p->in_iowait) { - delayacct_blkio_end(p); - atomic_dec(&task_rq(p)->nr_iowait); - } - #ifdef CONFIG_SMP /* * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be @@ -2291,6 +2291,11 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags, cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags, sibling_count_hint); if (task_cpu(p) != cpu) { + if (p->in_iowait) { + delayacct_blkio_end(p); + atomic_dec(&task_rq(p)->nr_iowait); + } + wake_flags |= WF_MIGRATED; psi_ttwu_dequeue(p); set_task_cpu(p, cpu);