Re: [PATCH v2 14/14] block: remove outdated AioContext locking comments

[Kevin Wolf <kwolf@xxxxxxxxxx>]

Am 05.12.2023 um 19:20 hat Stefan Hajnoczi geschrieben:
> The AioContext lock no longer exists.
> 
> There is one noteworthy change:
> 
>   - * More specifically, these functions use BDRV_POLL_WHILE(bs), which
>   - * requires the caller to be either in the main thread and hold
>   - * the BlockdriverState (bs) AioContext lock, or directly in the
>   - * home thread that runs the bs AioContext. Calling them from
>   - * another thread in another AioContext would cause deadlocks.
>   + * More specifically, these functions use BDRV_POLL_WHILE(bs), which 
> requires
>   + * the caller to be either in the main thread or directly in the home 
> thread
>   + * that runs the bs AioContext. Calling them from another thread in another
>   + * AioContext would cause deadlocks.
> 
> I am not sure whether deadlocks are still possible. Maybe they have just
> moved to the fine-grained locks that have replaced the AioContext. Since
> I am not sure if the deadlocks are gone, I have kept the substance
> unchanged and just removed mention of the AioContext.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>

I think the deadlock the comment refers to is that AIO_WAIT_WHILE() sits
in a blocking aio_poll() and nobody wakes it up because aio_wait_kick()
only wakes up the main thread. This deadlock still exists after removing
the AioContext lock, so the comment after your change looks right to me.

Reviewed-by: Kevin Wolf <kwolf@xxxxxxxxxx>