Re: [PATCH 1/2] linux-aio: fix unbalanced plugged counter in laio_io_unplug()

[Stefano Garzarella]

On Thu, Jun 09, 2022 at 05:47:11PM +0100, Stefan Hajnoczi wrote:
> Every laio_io_plug() call has a matching laio_io_unplug() call. There is
> a plugged counter that tracks the number of levels of plugging and
> allows for nesting.
>
> The plugged counter must reflect the balance between laio_io_plug() and
> laio_io_unplug() calls accurately. Otherwise I/O stalls occur since
> io_submit(2) calls are skipped while plugged.

We can add a Fixes tag:

Fixes: 68d7946648 ("linux-aio: add `dev_max_batch` parameter to 
laio_io_unplug()")

> Reported-by: Nikolay Tenev <nt@storpool.com>
> Cc: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> block/linux-aio.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block/linux-aio.c b/block/linux-aio.c
> index 4c423fcccf..6078da7e42 100644
> --- a/block/linux-aio.c
> +++ b/block/linux-aio.c
> @@ -363,8 +363,10 @@ void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s,
>                     uint64_t dev_max_batch)
> {
>     assert(s->io_q.plugged);
> +    s->io_q.plugged--;
> +
>     if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch) ||
> -        (--s->io_q.plugged == 0 &&
> +        (!s->io_q.plugged &&
>          !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending))) {
>         ioq_submit(s);
>     }
> --
> 2.36.1

Thanks for fixing this issue!

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>