| Message ID | 20211129034328.1604-1-longpeng2@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kvm/eventfd: fix the misleading comment in kvm_irqfd_assign | expand |
Am 29.11.21 um 04:43 schrieb Longpeng(Mike): > From: Longpeng <longpeng2@huawei.com> > > The comment above the invocation of vfs_poll() is misleading, move > it to the right place. > I think that the current variant is better. events is only used in that function to check for EPOLLIN, so the assignment and the if belong together from a "what am I doing here" perspective. > Fixes: 684a0b719ddb ("KVM: eventfd: Fix lock order inversion") > Signed-off-by: Longpeng <longpeng2@huawei.com> > --- > virt/kvm/eventfd.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 2ad013b..cd01814 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -406,12 +406,12 @@ bool __attribute__((weak)) kvm_arch_irqfd_route_changed( > > spin_unlock_irq(&kvm->irqfds.lock); > > + events = vfs_poll(f.file, &irqfd->pt); > + > /* > * 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 = vfs_poll(f.file, &irqfd->pt); > - > if (events & EPOLLIN) > schedule_work(&irqfd->inject); >
> -----Original Message----- > From: Christian Borntraeger [mailto:borntraeger@linux.ibm.com] > Sent: Tuesday, November 30, 2021 1:14 AM > To: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > <longpeng2@huawei.com>; pbonzini@redhat.com > Cc: cornelia.huck@de.ibm.com; kvm@vger.kernel.org; > linux-kernel@vger.kernel.org; Gonglei (Arei) <arei.gonglei@huawei.com> > Subject: Re: [PATCH] kvm/eventfd: fix the misleading comment in kvm_irqfd_assign > > > > Am 29.11.21 um 04:43 schrieb Longpeng(Mike): > > From: Longpeng <longpeng2@huawei.com> > > > > The comment above the invocation of vfs_poll() is misleading, move > > it to the right place. > > > I think that the current variant is better. > events is only used in that function to check for EPOLLIN, so the > assignment and the if belong together from a "what am I doing here" perspective. > Hi Christian, I think that add the irqfd->wait to the file's wait queue is much more important, the current variant may lead to ignoring it. Both of these two variants are supported in the current kernel: [1] https://elixir.bootlin.com/linux/latest/source/drivers/vfio/virqfd.c#L169 ``` events = vfs_poll(irqfd.file, &virqfd->pt); /* * Check if there was an event already pending on the eventfd * before we registered and trigger it as if we didn't miss it. */ if (events & EPOLLIN) { if ((!handler || handler(opaque, data)) && thread) schedule_work(&virqfd->inject); } ``` [2] https://elixir.bootlin.com/linux/latest/source/drivers/virt/acrn/irqfd.c#L161 ``` /* Check the pending event in this stage */ events = vfs_poll(f.file, &irqfd->pt); if (events & EPOLLIN) acrn_irqfd_inject(irqfd); ``` Since there's no any code changes, I agree to drop this unmeaning change. Thanks. > > Fixes: 684a0b719ddb ("KVM: eventfd: Fix lock order inversion") > > Signed-off-by: Longpeng <longpeng2@huawei.com> > > --- > > virt/kvm/eventfd.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > > index 2ad013b..cd01814 100644 > > --- a/virt/kvm/eventfd.c > > +++ b/virt/kvm/eventfd.c > > @@ -406,12 +406,12 @@ bool __attribute__((weak)) > kvm_arch_irqfd_route_changed( > > > > spin_unlock_irq(&kvm->irqfds.lock); > > > > + events = vfs_poll(f.file, &irqfd->pt); > > + > > /* > > * 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 = vfs_poll(f.file, &irqfd->pt); > > - > > if (events & EPOLLIN) > > schedule_work(&irqfd->inject); > >
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 2ad013b..cd01814 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -406,12 +406,12 @@ bool __attribute__((weak)) kvm_arch_irqfd_route_changed( spin_unlock_irq(&kvm->irqfds.lock); + events = vfs_poll(f.file, &irqfd->pt); + /* * 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 = vfs_poll(f.file, &irqfd->pt); - if (events & EPOLLIN) schedule_work(&irqfd->inject);