| Message ID | 1395079899-29239-2-git-send-email-cornelia.huck@de.ibm.com |
|---|---|
| State | New |
| Headers | show |
On 17/03/14 19:11, Cornelia Huck wrote: > 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> Do you still have the lockdep message somewhere? Looking at the patch and the description this makes sense. Even without irqfd for s390: Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Paolo, maybe this patch can go in independently from s390? Christian > --- > virt/kvm/eventfd.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > 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 @@ 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 >
On Mon, 17 Mar 2014 22:55:49 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote: > On 17/03/14 19:11, Cornelia Huck wrote: > > 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> > Do you still have the lockdep message somewhere? Unfortunately not, and it does not seem to be readily triggerable. > Looking at the patch and the description this makes sense. Even without > irqfd for s390: > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> > > Paolo, maybe this patch can go in independently from s390? > > Christian
Il 17/03/2014 22:55, Christian Borntraeger ha scritto: >> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com> > Do you still have the lockdep message somewhere? > Looking at the patch and the description this makes sense. Even without > irqfd for s390: > Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> > > Paolo, maybe this patch can go in independently from s390? Yes, that's fine. I'm applying it to kvm/queue. Paolo
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 @@ 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
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> --- virt/kvm/eventfd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)