Messages in this thread | | | Date | Fri, 3 Jul 2015 17:42:45 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched,kvm: Fix KVM preempt_notifier usage |
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On Fri, Jul 03, 2015 at 05:38:42PM +0200, Paolo Bonzini wrote: > So basically this. Can you reply with SoB and maybe Acked-by?
Ah, thanks for doing that!
> ------------- 8< --------------- > From: Peter Zijlstra <peterz@infradead.org> > Subject: [PATCH] sched, preempt_notifier: separate notifier registration from static_key inc/dec > > Commit 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers") > had two problems. First, the preempt-notifier API needs to sleep with the > addition of the static_key, we do however need to hold off preemption > while modifying the preempt notifier list, otherwise a preemption could > observe an inconsistent list state. KVM correctly registers and > unregisters preempt notifiers with preemption disabled, so the sleep > caused dmesg splats. > > Second, KVM registers and unregisters preemption notifiers very often > (in vcpu_load/vcpu_put). With a single uniprocessor guest the static key > would move between 0 and 1 continuously, hitting the slow path on every > userspace exit. > > To fix this, wrap the static_key inc/dec in a new API, and call it from > KVM. > > Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers") > Reported-by: Pontus Fuchs <pontus.fuchs@gmail.com> > Reported-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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