From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:36040)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1aYCWB-0004bw-Eg
	for qemu-devel@nongnu.org; Tue, 23 Feb 2016 07:56:45 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1aYCW6-0002xj-EQ
	for qemu-devel@nongnu.org; Tue, 23 Feb 2016 07:56:43 -0500
Received: from mx1.redhat.com ([209.132.183.28]:53482)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1aYCW6-0002xa-8c
	for qemu-devel@nongnu.org; Tue, 23 Feb 2016 07:56:38 -0500
Received: from int-mx10.intmail.prod.int.phx2.redhat.com
	(int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23])
	by mx1.redhat.com (Postfix) with ESMTPS id CEE84C0BA405
	for <qemu-devel@nongnu.org>; Tue, 23 Feb 2016 12:56:37 +0000 (UTC)
Date: Tue, 23 Feb 2016 20:56:35 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20160223125635.GC26812@ad.usersys.redhat.com>
References: <1455894643-16280-1-git-send-email-pbonzini@redhat.com>
	<20160223053926.GA23182@ad.usersys.redhat.com>
	<56CC299F.3040509@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <56CC299F.3040509@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] fixup! block-migration: acquire AioContext
	as necessary
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: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, mst@redhat.com

On Tue, 02/23 10:42, Paolo Bonzini wrote:
> 
> 
> On 23/02/2016 06:39, Fam Zheng wrote:
> > BTW, could you also explain the blk_mig_lock() question (*) I had?
> > 
> > *: https://lists.gnu.org/archive/html/qemu-devel/2016-02/msg03317.html
> 
> Sorry, missed that:
> 
> > 
> >> @@ -597,21 +627,28 @@ static void block_migration_cleanup(void *opaque)
> >>  {
> >>      BlkMigDevState *bmds;
> >>      BlkMigBlock *blk;
> >> +    AioContext *ctx;
> >>  
> >>      bdrv_drain_all();
> >>  
> >>      unset_dirty_tracking();
> >>  
> >> -    blk_mig_lock();
> > 
> > Why is it okay to skip the blk_mig_lock() for block_mig_state.bmds_list?
> 
> The bmds_list is not protected by blk_mig_lock:
> 
>     /* Written during setup phase.  Can be read without a lock.  */
>     int blk_enable;
>     int shared_base;
>     QSIMPLEQ_HEAD(bmds_list, BlkMigDevState) bmds_list;
>     int64_t total_sector_sum;
>     bool zero_blocks;
> 
> block_migration_cleanup is called from qemu_savevm_state_cleanup, when
> there can be no concurrency between the migration thread and the I/O
> thread.  In fact the call of qemu_savevm_state_cleanup might as well be
> moved out of the migration thread.

Thanks!

Fam