Messages in this thread Patch in this message | | | Date | Tue, 30 Jun 2015 04:10:24 -0700 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:sched/urgent] sched/preempt, kvm: Fix KVM preempt_notifier usage |
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Commit-ID: 6efde1d3716b7d055d3310bccba2df244cf430d7 Gitweb: http://git.kernel.org/tip/6efde1d3716b7d055d3310bccba2df244cf430d7 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Thu, 25 Jun 2015 14:55:14 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 30 Jun 2015 07:58:53 +0200
sched/preempt, kvm: Fix KVM preempt_notifier usage
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.
There is no reason to have preemption disabled in the caller, registering a preempt notifier is a purely task local affair.
Therefore move the preempt_disable into the functions and change the callers to a preemptible context.
Reported-and-Tested-by: Pontus Fuchs <pontus.fuchs@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Gleb Natapov <gleb@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Pontus Fuchs <pontus.fuchs@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers") Link: http://lkml.kernel.org/r/20150625125514.GA3644@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/sched/core.c | 11 +++++++++++ virt/kvm/kvm_main.c | 5 +++-- 2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c86935a..5bcf926 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2138,7 +2138,12 @@ static struct static_key preempt_notifier_key = STATIC_KEY_INIT_FALSE; void preempt_notifier_register(struct preempt_notifier *notifier) { static_key_slow_inc(&preempt_notifier_key); + /* + * Avoid preemption while changing the preempt notifier list. + */ + preempt_disable(); hlist_add_head(¬ifier->link, ¤t->preempt_notifiers); + preempt_enable(); } EXPORT_SYMBOL_GPL(preempt_notifier_register); @@ -2150,7 +2155,13 @@ EXPORT_SYMBOL_GPL(preempt_notifier_register); */ void preempt_notifier_unregister(struct preempt_notifier *notifier) { + /* + * Avoid preemption while changing the preempt notifier list. + */ + preempt_disable(); hlist_del(¬ifier->link); + preempt_enable(); + static_key_slow_dec(&preempt_notifier_key); } EXPORT_SYMBOL_GPL(preempt_notifier_unregister); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9097741..d7aafa0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -128,8 +128,9 @@ int vcpu_load(struct kvm_vcpu *vcpu) if (mutex_lock_killable(&vcpu->mutex)) return -EINTR; - cpu = get_cpu(); preempt_notifier_register(&vcpu->preempt_notifier); + + cpu = get_cpu(); kvm_arch_vcpu_load(vcpu, cpu); put_cpu(); return 0; @@ -139,8 +140,8 @@ void vcpu_put(struct kvm_vcpu *vcpu) { preempt_disable(); kvm_arch_vcpu_put(vcpu); - preempt_notifier_unregister(&vcpu->preempt_notifier); preempt_enable(); + preempt_notifier_unregister(&vcpu->preempt_notifier); mutex_unlock(&vcpu->mutex); }
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