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>
This commit is contained in:
Cornelia Huck 2014-03-17 19:11:35 +01:00 committed by Paolo Bonzini
parent 93c4adc7af
commit 684a0b719d

View file

@ -391,19 +391,19 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
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