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

[Stefan Hajnoczi]

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>
> ---
>  hw/block/virtio-blk.c | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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