On Tue, May 24, 2022 at 01:30:54PM -0400, Emanuele Giuseppe Esposito wrote:
> It seems that aio_wait_kick always required a memory barrier
> or atomic operation in the caller, but nobody actually
> took care of doing it.
>
> Let's put the barrier in the function instead, and pair it
> with another one in AIO_WAIT_WHILE. Read aio_wait_kick()
> comment for further explanation.
>
> Suggested-by: Paolo Bonzini <pbonz...@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
> ---
> include/block/aio-wait.h | 2 ++
> util/aio-wait.c | 16 +++++++++++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index b39eefb38d..54840f8622 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -81,6 +81,8 @@ extern AioWait global_aio_wait;
> AioContext *ctx_ = (ctx); \
> /* Increment wait_->num_waiters before evaluating cond. */ \
> qatomic_inc(&wait_->num_waiters); \
> + /* Paired with smp_mb in aio_wait_kick(). */ \
> + smp_mb(); \
IIRC qatomic_inc() ensures sequential consistency, isn't it enough here?
> if (ctx_ && in_aio_context_home_thread(ctx_)) { \
> while ((cond)) { \
> aio_poll(ctx_, true); \
Roman.
