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Re: [PATCH 1/2] virtio-blk: Acquire context while switching them on data
From: |
Sergio Lopez |
Subject: |
Re: [PATCH 1/2] virtio-blk: Acquire context while switching them on dataplane start |
Date: |
Wed, 9 Dec 2020 17:51:12 +0100 |
On Mon, Dec 07, 2020 at 04:37:53PM +0100, Kevin Wolf wrote:
> Am 04.12.2020 um 17:53 hat Sergio Lopez geschrieben:
> > On dataplane start, acquire the new AIO context before calling
> > 'blk_set_aio_context', releasing it immediately afterwards. This
> > prevents reaching the AIO context attach/detach notifier functions
> > without having acquired it first.
> >
> > It was also the only place where 'blk_set_aio_context' was called with
> > an unprotected AIO context.
> >
> > Signed-off-by: Sergio Lopez <slp@redhat.com>
> > ---
> > hw/block/dataplane/virtio-blk.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/hw/block/dataplane/virtio-blk.c
> > b/hw/block/dataplane/virtio-blk.c
> > index 37499c5564..034e43cb1f 100644
> > --- a/hw/block/dataplane/virtio-blk.c
> > +++ b/hw/block/dataplane/virtio-blk.c
> > @@ -214,7 +214,9 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
> > vblk->dataplane_started = true;
> > trace_virtio_blk_data_plane_start(s);
> >
> > + aio_context_acquire(s->ctx);
> > r = blk_set_aio_context(s->conf->conf.blk, s->ctx, &local_err);
> > + aio_context_release(s->ctx);
>
> bdrv_set_aio_context_ignore() is documented like this:
>
> * The caller must own the AioContext lock for the old AioContext of bs, but
> it
> * must not own the AioContext lock for new_context (unless new_context is the
> * same as the current context of bs).
Does that rule apply to blk_set_aio_context too? All use cases I can
find in the code are acquiring the new context:
hw/block/dataplane/xen-block.c:
719 void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
720 const unsigned int ring_ref[],
721 unsigned int nr_ring_ref,
722 unsigned int event_channel,
723 unsigned int protocol,
724 Error **errp)
725 {
...
811 aio_context_acquire(dataplane->ctx);
812 /* If other users keep the BlockBackend in the iothread, that's ok */
813 blk_set_aio_context(dataplane->blk, dataplane->ctx, NULL);
814 /* Only reason for failure is a NULL channel */
815 xen_device_set_event_channel_context(xendev, dataplane->event_channel,
816 dataplane->ctx, &error_abort);
817 aio_context_release(dataplane->ctx);
hw/scsi/virtio-scsi.c:
818 static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState
*dev,
819 Error **errp)
820 {
...
830 virtio_scsi_acquire(s);
831 ret = blk_set_aio_context(sd->conf.blk, s->ctx, errp);
832 virtio_scsi_release(s);
Thanks,
Sergio.
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