Re: [PULL 1/1] virtio-blk: avoid using ioeventfd state in irqfd conditional

[Kevin Wolf <kwolf@redhat.com>]

Am 08.02.2024 um 06:37 hat Michael Tokarev geschrieben:
> 06.02.2024 18:31, Stefan Hajnoczi :
> > Requests that complete in an IOThread use irqfd to notify the guest
> > while requests that complete in the main loop thread use the traditional
> > qdev irq code path. The reason for this conditional is that the irq code
> > path requires the BQL:
> > 
> >    if (s->ioeventfd_started && !s->ioeventfd_disabled) {
> >        virtio_notify_irqfd(vdev, req->vq);
> >    } else {
> >        virtio_notify(vdev, req->vq);
> >    }
> > 
> > There is a corner case where the conditional invokes the irq code path
> > instead of the irqfd code path:
> > 
> >    static void virtio_blk_stop_ioeventfd(VirtIODevice *vdev)
> >    {
> >        ...
> >        /*
> >         * Set ->ioeventfd_started to false before draining so that host notifiers
> >         * are not detached/attached anymore.
> >         */
> >        s->ioeventfd_started = false;
> > 
> >        /* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
> >        blk_drain(s->conf.conf.blk);
> > 
> > During blk_drain() the conditional produces the wrong result because
> > ioeventfd_started is false.
> > 
> > Use qemu_in_iothread() instead of checking the ioeventfd state.
> > 
> > Buglink: https://issues.redhat.com/browse/RHEL-15394
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Message-id: 20240122172625.415386-1-stefanha@redhat.com
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Cc qemu-stable?  This smells like a stable material, please let me know
> if it is not.

The patch email itself was CCed to qemu-stable and even contained a note
for backporting to stable:

https://lists.gnu.org/archive/html/qemu-block/2024-01/msg00278.html

It's only missing in the commit message. I'll add the Cc: line to
my pull request (for Stefan's pull request it seems too late because
Peter is already processing it, so we'll probably end up having both
versions in the git history).

Kevin