Re: [PATCH] virtio-blk: add missing AioContext lock

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 08, 2023 at 06:11:48AM -0500, Emanuele Giuseppe Esposito wrote:
> virtio_blk_update_config() calls blk_get_geometry and blk_getlength,
> and both functions eventually end up calling bdrv_poll_co when not
> running in a coroutine:
> - blk_getlength is a co_wrapper_mixed function
> - blk_get_geometry calls bdrv_get_geometry -> bdrv_nb_sectors, a
>   co_wrapper_mixed function too
> 
> Since we are not running in a coroutine, we need to take s->blk
> AioContext lock, otherwise bdrv_poll_co will inevitably call
> AIO_WAIT_WHILE and therefore try to un unlock() an AioContext lock
> that was never acquired.
> 
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2167838
> 
> Steps to reproduce the issue: simply boot a VM with
> -object '{"qom-type":"iothread","id":"iothread1"}' \
> -blockdev '{"driver":"file","filename":"$QCOW2","aio":"native","node-name":"libvirt-1-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true,"discard":"unmap"}' \
> -blockdev '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":"libvirt-1-storage"}' \
> -device virtio-blk-pci,iothread=iothread1,drive=libvirt-1-format,id=virtio-disk0,bootindex=1,write-cache=on
> 
> and observe that it will fail not manage to boot with "qemu_mutex_unlock_impl: Operation not permitted"
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>


looks reasonable

Acked-by: Michael S. Tsirkin <mst@redhat.com>

merge in block tree pls.

> ---
>  hw/block/virtio-blk.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 1762517878..cefca93b31 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -894,6 +894,10 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>      uint64_t capacity;
>      int64_t length;
>      int blk_size = conf->logical_block_size;
> +    AioContext *ctx;
> +
> +    ctx = blk_get_aio_context(s->blk);
> +    aio_context_acquire(ctx);
>  
>      blk_get_geometry(s->blk, &capacity);
>      memset(&blkcfg, 0, sizeof(blkcfg));
> @@ -917,6 +921,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config)
>       * per track (cylinder).
>       */
>      length = blk_getlength(s->blk);
> +    aio_context_release(ctx);
>      if (length > 0 && length / conf->heads / conf->secs % blk_size) {
>          blkcfg.geometry.sectors = conf->secs & ~s->sector_mask;
>      } else {
> -- 
> 2.39.1