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| author | Kosuke Tatsukawa <tatsu@ab.jp.nec.com> | 2015-10-09 12:21:55 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-10-14 16:41:08 +0200 |
| commit | 6003a4201077da41427dae5e71bb2f31dfdc0c10 (patch) | |
| tree | 203a2877d5c8b8d6dfdfe364d5744c032cb01450 /virt | |
| parent | 13db77347db175a68edd58a79963cdf5cb3a9607 (diff) | |
| download | linux-6003a4201077da41427dae5e71bb2f31dfdc0c10.tar.bz2 | |
kvm: fix waitqueue_active without memory barrier in virt/kvm/async_pf.c
async_pf_execute() seems to be missing a memory barrier which might
cause the waker to not notice the waiter and miss sending a wake_up as
in the following figure.
async_pf_execute kvm_vcpu_block
------------------------------------------------------------------------
spin_lock(&vcpu->async_pf.lock);
if (waitqueue_active(&vcpu->wq))
/* The CPU might reorder the test for
the waitqueue up here, before
prior writes complete */
prepare_to_wait(&vcpu->wq, &wait,
TASK_INTERRUPTIBLE);
/*if (kvm_vcpu_check_block(vcpu) < 0) */
/*if (kvm_arch_vcpu_runnable(vcpu)) { */
...
return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
!vcpu->arch.apf.halted)
|| !list_empty_careful(&vcpu->async_pf.done)
...
return 0;
list_add_tail(&apf->link,
&vcpu->async_pf.done);
spin_unlock(&vcpu->async_pf.lock);
waited = true;
schedule();
------------------------------------------------------------------------
The attached patch adds the missing memory barrier.
I found this issue when I was looking through the linux source code
for places calling waitqueue_active() before wake_up*(), but without
preceding memory barriers, after sending a patch to fix a similar
issue in drivers/tty/n_tty.c (Details about the original issue can be
found here: https://lkml.org/lkml/2015/9/28/849).
Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/async_pf.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 44660aee335f..77d42be6970e 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -94,6 +94,10 @@ static void async_pf_execute(struct work_struct *work) trace_kvm_async_pf_completed(addr, gva); + /* + * This memory barrier pairs with prepare_to_wait's set_current_state() + */ + smp_mb(); if (waitqueue_active(&vcpu->wq)) wake_up_interruptible(&vcpu->wq); |