Re: [PATCH 1/2] aio: allow to wait for coroutine pool from different coroutine

[Vladimir Sementsov-Ogievskiy]

10.06.2020 17:41, Denis V. Lunev wrote:
> The patch preserves the constraint that the only waiter is allowed.
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> CC: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>   block/aio_task.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/block/aio_task.c b/block/aio_task.c
> index 88989fa248..f338049147 100644
> --- a/block/aio_task.c
> +++ b/block/aio_task.c
> @@ -27,7 +27,7 @@
>   #include "block/aio_task.h"
>   
>   struct AioTaskPool {
> -    Coroutine *main_co;
> +    Coroutine *wake_co;
>       int status;
>       int max_busy_tasks;
>       int busy_tasks;
> @@ -54,15 +54,15 @@ static void coroutine_fn aio_task_co(void *opaque)
>   
>       if (pool->waiting) {
>           pool->waiting = false;
> -        aio_co_wake(pool->main_co);
> +        aio_co_wake(pool->wake_co);
>       }
>   }
>   
>   void coroutine_fn aio_task_pool_wait_one(AioTaskPool *pool)
>   {
>       assert(pool->busy_tasks > 0);
> -    assert(qemu_coroutine_self() == pool->main_co);
>   
> +    pool->wake_co = qemu_coroutine_self();
>       pool->waiting = true;
>       qemu_coroutine_yield();
>   
> @@ -98,7 +98,7 @@ AioTaskPool *coroutine_fn aio_task_pool_new(int max_busy_tasks)
>   {
>       AioTaskPool *pool = g_new0(AioTaskPool, 1);
>   
> -    pool->main_co = qemu_coroutine_self();
> +    pool->wake_co = NULL;
>       pool->max_busy_tasks = max_busy_tasks;
>   
>       return pool;

With such approach, if several coroutines will wait simultaneously, the only 
one will be finally woken and other will hang.

I think, we should use CoQueue here: CoQueue instead of wake_co, 
qemu_co_queue_wait in wait_one, and qemu_co_queue_next instead of aio_co_wake.


--
Best regards,
Vladimir