Re: [PATCH 03/12] aio: make aio_context_acquire()/aio_context_release() a no-op

[Eric Blake]

On Wed, Nov 29, 2023 at 02:55:44PM -0500, Stefan Hajnoczi wrote:
> aio_context_acquire()/aio_context_release() has been replaced by
> fine-grained locking to protect state shared by multiple threads. The
> AioContext lock still plays the role of balancing locking in
> AIO_WAIT_WHILE() and many functions in QEMU either require that the
> AioContext lock is held or not held for this reason. In other words, the
> AioContext lock is purely there for consistency with itself and serves
> no real purpose anymore.
> 
> Stop actually acquiring/releasing the lock in
> aio_context_acquire()/aio_context_release() so that subsequent patches
> can remove callers across the codebase incrementally.
> 
> I have performed "make check" and qemu-iotests stress tests across
> x86-64, ppc64le, and aarch64 to confirm that there are no failures as a
> result of eliminating the lock.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  util/async.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/util/async.c b/util/async.c
> index 8f90ddc304..04ee83d220 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -725,12 +725,12 @@ void aio_context_unref(AioContext *ctx)
>  
>  void aio_context_acquire(AioContext *ctx)
>  {
> -    qemu_rec_mutex_lock(&ctx->lock);
> +    /* TODO remove this function */
>  }
>  
>  void aio_context_release(AioContext *ctx)
>  {
> -    qemu_rec_mutex_unlock(&ctx->lock);
> +    /* TODO remove this function */
>  }
>  
>  QEMU_DEFINE_STATIC_CO_TLS(AioContext *, my_aiocontext)
> -- 
> 2.42.0

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

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