Re: [RFC PATCH 11/15] jobs: remove aiocontext locks since the functions are under BQL

[Vladimir Sementsov-Ogievskiy]

Hmm. subject looks like it's safe to remove aiocontext locks from any qmp 
command?

For example, commit 91005a495e228eb added aiocontext locks back to qmp bitmap 
add/remove commands because otherwise they crashed.

So, I'm not sure that being under BQL is enough to drop aiocontext locking..


29.10.2021 19:39, Emanuele Giuseppe Esposito wrote:
> In preparation to the job_lock/unlock patch, remove these
> aiocontext locks.
> The main reason these two locks are removed here is because
> they are inside a loop iterating on the jobs list. Once the
> job_lock is added, it will have to protect the whole loop,
> wrapping also the aiocontext acquire/release.
>
> We don't want this, as job_lock can only be *wrapped by*
> the aiocontext lock, and not vice-versa, to avoid deadlocks.
>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>   blockdev.c | 4 ----
>   job-qmp.c  | 4 ----
>   2 files changed, 8 deletions(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index d9bf842a81..67b55eec11 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3719,15 +3719,11 @@ BlockJobInfoList *qmp_query_block_jobs(Error **errp)
>   
>       for (job = block_job_next(NULL); job; job = block_job_next(job)) {
>           BlockJobInfo *value;
> -        AioContext *aio_context;
>   
>           if (block_job_is_internal(job)) {
>               continue;
>           }
> -        aio_context = blk_get_aio_context(job->blk);
> -        aio_context_acquire(aio_context);
>           value = block_job_query(job, errp);
> -        aio_context_release(aio_context);
>           if (!value) {
>               qapi_free_BlockJobInfoList(head);
>               return NULL;
> diff --git a/job-qmp.c b/job-qmp.c
> index 829a28aa70..a6774aaaa5 100644
> --- a/job-qmp.c
> +++ b/job-qmp.c
> @@ -173,15 +173,11 @@ JobInfoList *qmp_query_jobs(Error **errp)
>   
>       for (job = job_next(NULL); job; job = job_next(job)) {
>           JobInfo *value;
> -        AioContext *aio_context;
>   
>           if (job_is_internal(job)) {
>               continue;
>           }
> -        aio_context = job->aio_context;
> -        aio_context_acquire(aio_context);
>           value = job_query_single(job, errp);
> -        aio_context_release(aio_context);
>           if (!value) {
>               qapi_free_JobInfoList(head);
>               return NULL;


--
Best regards,
Vladimir