On Wed, Jun 10, 2015 at 02:38:16PM +0300, Alexander Yarygin wrote:
> Each call of the virtio_blk_reset() function calls blk_drain_all(),
> which works for all existing BlockDriverStates, while draining only
> one is needed.
>
> This patch replaces blk_drain_all() by blk_drain() in virtio_blk_reset().
>
> Cc: Christian Borntraeger <borntrae...@de.ibm.com>
> Cc: Cornelia Huck <cornelia.h...@de.ibm.com>
> Cc: Kevin Wolf <kw...@redhat.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Stefan Hajnoczi <stefa...@redhat.com>
> Signed-off-by: Alexander Yarygin <yary...@linux.vnet.ibm.com>
> ---
> hw/block/virtio-blk.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index e6afe97..2009092 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -652,15 +652,16 @@ static void virtio_blk_reset(VirtIODevice *vdev)
> {
> VirtIOBlock *s = VIRTIO_BLK(vdev);
>
> - if (s->dataplane) {
> - virtio_blk_data_plane_stop(s->dataplane);
> - }
> -
> /*
> * This should cancel pending requests, but can't do nicely until there
> * are per-device request lists.
> */
> - blk_drain_all();
> + blk_drain(s->blk);
> +
> + if (s->dataplane) {
> + virtio_blk_data_plane_stop(s->dataplane);
> + }
This is unsafe now. virtio_blk_reset() is called from the vcpu thread
while the virtqueue processing may be running in an IOThread.
blk_drain() does not acquire AioContext so it races with the IOThread.
Try:
ctx = bdrv_get_aio_context(s->blk);
aio_context_acquire(ctx);
blk_drain(s->blk);
if (s->dataplane) {
virtio_blk_data_plane_stop(s->dataplane);
}
aio_context_release(ctx);
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