From: Michael Tokarev <mjt@tls.msk.ru>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
Kevin Wolf <kwolf@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Hanna Reitz <hreitz@redhat.com>,
qemu-block@nongnu.org, qemu-stable <qemu-stable@nongnu.org>
Subject: Re: [PULL 1/1] virtio-blk: avoid using ioeventfd state in irqfd conditional
Date: Thu, 8 Feb 2024 08:37:37 +0300 [thread overview]
Message-ID: <9393f1f7-9939-4640-aa43-f7df042a8ee9@tls.msk.ru> (raw)
In-Reply-To: <20240206153105.81868-2-stefanha@redhat.com>
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.
(And yes I've seen it also included in another pullreq)
Thanks,
/mjt
next prev parent reply other threads:[~2024-02-08 5:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-06 15:31 [PULL 0/1] Block patches Stefan Hajnoczi
2024-02-06 15:31 ` [PULL 1/1] virtio-blk: avoid using ioeventfd state in irqfd conditional Stefan Hajnoczi
2024-02-08 5:37 ` Michael Tokarev [this message]
2024-02-08 8:42 ` Kevin Wolf
2024-02-08 9:01 ` Michael Tokarev
2024-02-07 22:19 ` [PULL 0/1] Block patches Kevin Wolf
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