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 <[email protected]> > 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 <[email protected]> > Reported-by: Takashi Iwai <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
