Re: [PATCH v2 3/6] block: convert bdrv_graph_wrlock() to AIO_WAIT_WHILE_UNLOCKED()

[Wilfred Mallawa]

On Thu, 2023-03-09 at 14:08 -0500, Stefan Hajnoczi wrote:
> The following conversion is safe and does not change behavior:
> 
>      GLOBAL_STATE_CODE();
>      ...
>   -  AIO_WAIT_WHILE(qemu_get_aio_context(), ...);
>   +  AIO_WAIT_WHILE_UNLOCKED(NULL, ...);
> 
> Since we're in GLOBAL_STATE_CODE(), qemu_get_aio_context() is our
> home
> thread's AioContext. Thus AIO_WAIT_WHILE() does not unlock the
> AioContext:
> 
>   if (ctx_ && in_aio_context_home_thread(ctx_)) {                \
>       while ((cond)) {                                           \
>           aio_poll(ctx_, true);                                  \
>           waited_ = true;                                        \
>       }                                                          \
> 
> And that means AIO_WAIT_WHILE_UNLOCKED(NULL, ...) can be substituted.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/graph-lock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
> 
> diff --git a/block/graph-lock.c b/block/graph-lock.c
> index 454c31e691..639526608f 100644
> --- a/block/graph-lock.c
> +++ b/block/graph-lock.c
> @@ -127,7 +127,7 @@ void bdrv_graph_wrlock(void)
>           * reader lock.
>           */
>          qatomic_set(&has_writer, 0);
> -        AIO_WAIT_WHILE(qemu_get_aio_context(), reader_count() >= 1);
> +        AIO_WAIT_WHILE_UNLOCKED(NULL, reader_count() >= 1);
>          qatomic_set(&has_writer, 1);
>  
>          /*