Commit 4c0b4bc6 authored Sep 13, 2017 by Davidlohr Bueso Committed by Paolo Bonzini Sep 15, 2017

kvm,mips: Fix potential swait_active() races



For example, the following could occur, making us miss a wakeup:

CPU0					CPU1
kvm_vcpu_block				kvm_mips_comparecount_func
					  [L] swait_active(&vcpu->wq)
  [S] prepare_to_swait(&vcpu->wq)
  [L] if (!kvm_vcpu_has_pending_timer(vcpu))
         schedule()                       [S] queue_timer_int(vcpu)

Ensure that the swait_active() check is not hoisted over the interrupt.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 267ad7bc

arch/mips/kvm/mips.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -514,7 +514,7 @@ int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu,

		dvcpu->arch.wait = 0;

		if (swait_active(&dvcpu->wq))
		if (swq_has_sleeper(&dvcpu->wq))
		swake_up(&dvcpu->wq);

		return 0;
		@@ -1179,7 +1179,7 @@ static void kvm_mips_comparecount_func(unsigned long data)
		kvm_mips_callbacks->queue_timer_int(vcpu);

		vcpu->arch.wait = 0;
		if (swait_active(&vcpu->wq))
		if (swq_has_sleeper(&vcpu->wq))
		swake_up(&vcpu->wq);
		}

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