Re: AIO_WAIT_WHILE questions

[Markus Armbruster]

Cc'ing people based on output of "scripts/get_maintainer.pl -f
include/block/aio-wait.h".

Dietmar Maurer <address@hidden> writes:

> Hi all,
>
> I have a question about AIO_WAIT_WHILE. The docs inside the code say:
>
>  * The caller's thread must be the IOThread that owns @ctx or the main loop
>  * thread (with @ctx acquired exactly once).
>
> I wonder if that "with @ctx acquired exactly once" is always required?
>
> I have done a quick test (see code below) and this reveals that the condition 
> is not
> always met.
>
> Or is my test wrong (or the docs)?
>
> ---debug helper---
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index afeeb18f95..cf78dca9f9 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -82,6 +82,8 @@ extern AioWait global_aio_wait;
>      atomic_inc(&wait_->num_waiters);                               \
>      if (ctx_ && in_aio_context_home_thread(ctx_)) {                \
>          while ((cond)) {                                           \
> +            printf("AIO_WAIT_WHILE %p %d\n", ctx, ctx_->lock_count);     \
> +            assert(ctx_->lock_count == 1);                   \
>              aio_poll(ctx_, true);                                  \
>              waited_ = true;                                        \
>          }                                                          \
> diff --git a/include/block/aio.h b/include/block/aio.h
> index cb1989105a..51ef20e2f0 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -125,6 +125,7 @@ struct AioContext {
>  
>      /* Used by AioContext users to protect from multi-threaded access.  */
>      QemuRecMutex lock;
> +    int lock_count;
>  
>      /* The list of registered AIO handlers.  Protected by ctx->list_lock. */
>      AioHandlerList aio_handlers;
> diff --git a/util/async.c b/util/async.c
> index b94518b948..9804c6c64f 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -594,9 +594,11 @@ void aio_context_unref(AioContext *ctx)
>  void aio_context_acquire(AioContext *ctx)
>  {
>      qemu_rec_mutex_lock(&ctx->lock);
> +    ctx->lock_count++;
>  }
>  
>  void aio_context_release(AioContext *ctx)
>  {
> +    ctx->lock_count--;
>      qemu_rec_mutex_unlock(&ctx->lock);
>  }