KVM: eventfd: Fix lock order inversion.
When registering a new irqfd, we call its ->poll method to collect any
event that might have previously been pending so that we can trigger it.
This is done under the kvm->irqfds.lock, which means the eventfd's ctx
lock is taken under it.
However, if we get a POLLHUP in irqfd_wakeup, we will be called with the
ctx lock held before getting the irqfds.lock to deactivate the irqfd,
causing lockdep to complain.
Calling the ->poll method does not really need the irqfds.lock, so let's
just move it after we've given up the irqfds.lock in kvm_irqfd_assign().
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index abe4d60..29c2a04 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -391,19 +391,19 @@
lockdep_is_held(&kvm->irqfds.lock));
irqfd_update(kvm, irqfd, irq_rt);
- events = f.file->f_op->poll(f.file, &irqfd->pt);
-
list_add_tail(&irqfd->list, &kvm->irqfds.items);
+ spin_unlock_irq(&kvm->irqfds.lock);
+
/*
* Check if there was an event already pending on the eventfd
* before we registered, and trigger it as if we didn't miss it.
*/
+ events = f.file->f_op->poll(f.file, &irqfd->pt);
+
if (events & POLLIN)
schedule_work(&irqfd->inject);
- spin_unlock_irq(&kvm->irqfds.lock);
-
/*
* do not drop the file until the irqfd is fully initialized, otherwise
* we might race against the POLLHUP