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

[Denis V. Lunev]

On 6/10/20 6:10 PM, Vladimir Sementsov-Ogievskiy wrote:
> 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.
>
>
I will make a check, but for now it would be enough to
add
  assert(!pool->waiting);
at the beginning of aio_task_pool_wait_one

Den