Re: [Qemu-devel] [RFC PATCH 6/9] blkdebug: Implement .cancel_async

[Stefan Hajnoczi]

On Thu, Aug 21, 2014 at 07:56:53PM +0800, Fam Zheng wrote:
> @@ -446,12 +439,25 @@ static void error_callback_bh(void *opaque)
>      qemu_aio_release(acb);
>  }
>  
> +static void blkdebug_aio_cancel_async(BlockDriverAIOCB *blockacb)
> +{
> +    BlkdebugAIOCB *acb = container_of(blockacb, BlkdebugAIOCB, common);
> +    blockacb->cb(blockacb->opaque, -ECANCELED);
> +    qemu_aio_release(acb);
> +}
> +
>  static void blkdebug_aio_cancel(BlockDriverAIOCB *blockacb)
>  {
>      BlkdebugAIOCB *acb = container_of(blockacb, BlkdebugAIOCB, common);
>      qemu_aio_release(acb);
>  }

Both blkdebug_aio_cancel() and blkdebug_aio_cancel_async() look
incorrect.  It is not safe to release acb because the
error_callback_bh() BH may still be scheduled.

I guess we don't hit this problem because the error injection happens
within the same event loop iteration.  In practice no one ever calls
blkdebug_aio_cancel()?

Stefan

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