Re: [PATCH for-6.2 v3 01/12] job: Context changes in job_completed_txn_abort()

[Eric Blake <eblake@redhat.com>]

On Fri, Aug 06, 2021 at 11:38:48AM +0200, Max Reitz wrote:
> Finalizing the job may cause its AioContext to change.  This is noted by
> job_exit(), which points at job_txn_apply() to take this fact into
> account.
> 
> However, job_completed() does not necessarily invoke job_txn_apply()
> (through job_completed_txn_success()), but potentially also
> job_completed_txn_abort().  The latter stores the context in a local
> variable, and so always acquires the same context at its end that it has
> released in the beginning -- which may be a different context from the
> one that job_exit() releases at its end.  If it is different, qemu
> aborts ("qemu_mutex_unlock_impl: Operation not permitted").

Is this a bug fix that needs to make it into 6.1?

> 
> Drop the local @outer_ctx variable from job_completed_txn_abort(), and
> instead re-acquire the actual job's context at the end of the function,
> so job_exit() will release the same.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  job.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)

The commit message makes sense, and does a good job at explaining the
change.  I'm still a bit fuzzy on how jobs are supposed to play nice
with contexts, but since your patch matches the commit message, I'm
happy to give:

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

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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