Re: [PATCH for-9.0] mirror: Don't call job_pause_point() under graph lock

[Eric Blake]

On Wed, Mar 13, 2024 at 04:30:00PM +0100, Kevin Wolf wrote:
> Calling job_pause_point() while holding the graph reader lock
> potentially results in a deadlock: bdrv_graph_wrlock() first drains
> everything, including the mirror job, which pauses it. The job is only
> unpaused at the end of the drain section, which is when the graph writer
> lock has been successfully taken. However, if the job happens to be
> paused at a pause point where it still holds the reader lock, the writer
> lock can't be taken as long as the job is still paused.
> 
> Mark job_pause_point() as GRAPH_UNLOCKED and fix mirror accordingly.
> 
> Cc: qemu-stable@nongnu.org
> Buglink: https://issues.redhat.com/browse/RHEL-28125
> Fixes: 004915a96a7a40e942ac85e6d22518cbcd283506
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/qemu/job.h |  2 +-
>  block/mirror.c     | 10 ++++++----
>  2 files changed, 7 insertions(+), 5 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org