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sched/fair: Fix external p->on_rq users

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Sean noted that ever since commit 152e11f6df ("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: 152e11f6df ("sched/fair: Implement delayed dequeue")
Reported-by: Sean Christopherson <seanjc@google.com>
Tested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20241010091843.GK33184@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra
2024-10-10 11:38:10 +02:00
committed by Ingo Molnar
parent c650812419
commit cd9626e9eb
8 changed files with 38 additions and 7 deletions
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virt/kvm/kvm_main.c
+1 -1
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@@ -6387,7 +6387,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
WRITE_ONCE(vcpu->scheduled_out, true);
if (current->on_rq && vcpu->wants_to_run) {
if (task_is_runnable(current) && vcpu->wants_to_run) {
WRITE_ONCE(vcpu->preempted, true);
WRITE_ONCE(vcpu->ready, true);
}