From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:47275)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <quintela@redhat.com>) id 1ZrSjm-00016k-Ds
	for qemu-devel@nongnu.org; Wed, 28 Oct 2015 11:34:07 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <quintela@redhat.com>) id 1ZrSjh-00047e-1V
	for qemu-devel@nongnu.org; Wed, 28 Oct 2015 11:34:06 -0400
From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <1446044465-19312-5-git-send-email-den@openvz.org> (Denis
	V. Lunev's message of "Wed, 28 Oct 2015 18:01:05 +0300")
References: <1446044465-19312-1-git-send-email-den@openvz.org>
	<1446044465-19312-5-git-send-email-den@openvz.org>
Date: Wed, 28 Oct 2015 16:33:58 +0100
Message-ID: <871tcf80t5.fsf@neno.neno>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [Qemu-devel] [PATCH 4/4] migration: add missed
	aio_context_acquire into HMP snapshot code
Reply-To: quintela@redhat.com
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Denis V. Lunev" <den@openvz.org>
Cc: Amit Shah <amit.shah@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, qemu-stable@nongnu.org

"Denis V. Lunev" <den@openvz.org> wrote:
> aio_context should be locked in the similar way as was done in QMP
> snapshot creation in the other case there are a lot of possible
> troubles if native AIO mode is enabled for disk.
>
> - the command can hang (HMP thread) with missed wakeup (the operation is
>   actually complete)
>     io_submit
>     ioq_submit
>     laio_submit
>     raw_aio_submit
>     raw_aio_readv
>     bdrv_co_io_em
>     bdrv_co_readv_em
>     bdrv_aligned_preadv
>     bdrv_co_do_preadv
>     bdrv_co_do_readv
>     bdrv_co_readv
>     qcow2_co_readv
>     bdrv_aligned_preadv
>     bdrv_co_do_pwritev
>     bdrv_rw_co_entry
>
> - QEMU can assert in coroutine re-enter
>     __GI_abort
>     qemu_coroutine_enter
>     bdrv_co_io_em_complete
>     qemu_laio_process_completion
>     qemu_laio_completion_bh
>     aio_bh_poll
>     aio_dispatch
>     aio_poll
>     iothread_run
>
> qemu_fopen_bdrv and bdrv_fclose are used in real snapshot operations only
> along with block drivers. This change should influence only HMP snapshot
> operations.
>
> AioContext lock is reqursive. Thus nested locking should not be a problem.
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Juan Quintela <quintela@redhat.com>
> CC: Amit Shah <amit.shah@redhat.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

Should this one go through the block layer?  I guess that the block
layer, but otherwise, I will get it.


> -    return bdrv_flush(opaque);

> +    BlockDriverState *bs = (BlockDriverState *)opaque;

Cast not needed.

BlockDriverState * bs = opaque;

is even better.

Thanks, Juan.