[PATCH 3/6] sched,perf,kvm: Fix preemption condition
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From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-06-02 13:31:28
Also in:
cgroups, dm-devel, kvm, linux-fsdevel, linux-mm, linux-perf-users, linux-pm, linux-usb, lkml, netdev, rcu
Subsystem:
kernel virtual machine (kvm), performance events subsystem, the rest · Maintainers:
Paolo Bonzini, Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds
When ran from the sched-out path (preempt_notifier or perf_event), p->state is irrelevant to determine preemption. You can get preempted with !task_is_running() just fine. The right indicator for preemption is if the task is still on the runqueue in the sched-out path. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/events/core.c | 7 +++---- virt/kvm/kvm_main.c | 2 +- 2 files changed, 4 insertions(+), 5 deletions(-)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c@@ -8568,13 +8568,12 @@ static void perf_event_switch(struct tas }, }; - if (!sched_in && task->state == TASK_RUNNING) + if (!sched_in && current->on_rq) { switch_event.event_id.header.misc |= PERF_RECORD_MISC_SWITCH_OUT_PREEMPT; + } - perf_iterate_sb(perf_event_switch_output, - &switch_event, - NULL); + perf_iterate_sb(perf_event_switch_output, &switch_event, NULL); } /* --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c
@@ -4869,7 +4869,7 @@ static void kvm_sched_out(struct preempt { struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); - if (current->state == TASK_RUNNING) { + if (current->on_rq) { WRITE_ONCE(vcpu->preempted, true); WRITE_ONCE(vcpu->ready, true); }