Re: [Qemu-block] [Qemu-devel] [PATCH 05/17] block: access wakeup with atomic ops

[Fam Zheng]

On Thu, 04/20 14:00, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  block/io.c                | 3 ++-
>  block/nfs.c               | 4 +++-
>  block/sheepdog.c          | 3 ++-
>  include/block/block.h     | 5 +++--
>  include/block/block_int.h | 4 ++--
>  5 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 869322a..3b2ede9 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -501,7 +501,8 @@ static void dummy_bh_cb(void *opaque)
>  
>  void bdrv_wakeup(BlockDriverState *bs)
>  {
> -    if (bs->wakeup) {
> +    /* The barrier (or an atomic op) is in the caller.  */

Why not add a barrier here so that callers don't need to worry about that?

> +    if (atomic_read(&bs->wakeup)) {
>          aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
>      }
>  }

Fam