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Peter Zijlstra 2ecd9d29ab sched, preempt_notifier: separate notifier registration from static_key inc/dec 
Commit 1cde2930e1 ("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: 1cde2930e1 ("sched/preempt: Add static_key() to preempt_notifiers")
Reported-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Reported-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
 		2015-07-03 18:55:00 +02:00
..
arm arm64 updates for 4.2, mostly refactoring/clean-up: 2015-06-24 10:02:15 -07:00
Kconfig KVM: Disable compat ioctl for s390 2015-02-09 12:44:14 +01:00
async_pf.c mm: gup: kvm use get_user_pages_unlocked 2015-02-11 17:06:05 -08:00
async_pf.h KVM: fix checkpatch.pl errors in kvm/async_pf.h 2015-06-19 17:16:25 +02:00
coalesced_mmio.c KVM: move iodev.h from virt/kvm/ to include/kvm 2015-03-26 21:43:12 +00:00
coalesced_mmio.h KVM: fix checkpatch.pl errors in kvm/coalesced_mmio.h 2015-06-19 17:16:26 +02:00
eventfd.c KVM: move iodev.h from virt/kvm/ to include/kvm 2015-03-26 21:43:12 +00:00
irqchip.c kvm: irqchip: Break up high order allocations of kvm_irq_routing_table 2015-06-19 17:16:25 +02:00
kvm_main.c sched, preempt_notifier: separate notifier registration from static_key inc/dec 2015-07-03 18:55:00 +02:00
vfio.c kvm: vfio: fix unregister kvm_device_ops of vfio 2014-10-24 13:30:47 +02:00
vfio.h kvm: vfio: fix unregister kvm_device_ops of vfio 2014-10-24 13:30:47 +02:00