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Subject[PATCH 4/7] kvm,x86: Fix apf_task_wake_one() wq serialization
Date
During code inspection, the following potential race was seen:

CPU0 CPU1
kvm_async_pf_task_wait apf_task_wake_one
[L] swait_active(&n->wq)
[S] prepare_to_swait(&n.wq)
[L] if (!hlist_unhahed(&n.link))
schedule() [S] hlist_del_init(&n->link);

Properly serialize swait_active() checks such that a wakeup is
not missed.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
arch/x86/kernel/kvm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 874827b0d7ca..aa60a08b65b1 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -180,7 +180,7 @@ static void apf_task_wake_one(struct kvm_task_sleep_node *n)
hlist_del_init(&n->link);
if (n->halted)
smp_send_reschedule(n->cpu);
- else if (swait_active(&n->wq))
+ else if (swq_has_sleeper(&n->wq))
swake_up(&n->wq);
}

--
2.12.0
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