From cd9626e9ebc77edec33023fe95dab4b04ffc819d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 10 Oct 2024 11:38:10 +0200 Subject: sched/fair: Fix external p->on_rq users Sean noted that ever since commit 152e11f6df29 ("sched/fair: Implement delayed dequeue") KVM's preemption notifiers have started mis-classifying preemption vs blocking. Notably p->on_rq is no longer sufficient to determine if a task is runnable or blocked -- the aforementioned commit introduces tasks that remain on the runqueue even through they will not run again, and should be considered blocked for many cases. Add the task_is_runnable() helper to classify things and audit all external users of the p->on_rq state. Also add a few comments. Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue") Reported-by: Sean Christopherson Tested-by: Sean Christopherson Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20241010091843.GK33184@noisy.programming.kicks-ass.net --- kernel/freezer.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'kernel/freezer.c') diff --git a/kernel/freezer.c b/kernel/freezer.c index 44bbd7dbd2c8..8d530d0949ff 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -109,7 +109,12 @@ static int __set_task_frozen(struct task_struct *p, void *arg) { unsigned int state = READ_ONCE(p->__state); - if (p->on_rq) + /* + * Allow freezing the sched_delayed tasks; they will not execute until + * ttwu() fixes them up, so it is safe to swap their state now, instead + * of waiting for them to get fully dequeued. + */ + if (task_is_runnable(p)) return 0; if (p != current && task_curr(p)) -- cgit v1.2.3