From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34419) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1covPi-0002ah-4t for qemu-devel@nongnu.org; Fri, 17 Mar 2017 13:11:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1covPf-0004d5-0T for qemu-devel@nongnu.org; Fri, 17 Mar 2017 13:11:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42718) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1covPe-0004cN-Mo for qemu-devel@nongnu.org; Fri, 17 Mar 2017 13:11:38 -0400 References: From: Paolo Bonzini Message-ID: Date: Fri, 17 Mar 2017 18:11:35 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ed Swierk , Fam Zheng , Kevin Wolf Cc: qemu-devel@nongnu.org On 17/03/2017 17:55, Ed Swierk wrote: > I'm running into the same problem taking an external snapshot with a > virtio-blk drive with iothread, so it's not specific to virtio-scsi. > Run a Linux guest on qemu master > > qemu-system-x86_64 -nographic -enable-kvm -monitor > telnet:0.0.0.0:1234,server,nowait -m 1024 -object > iothread,id=iothread1 -drive file=/x/drive.qcow2,if=none,id=drive0 > -device virtio-blk-pci,iothread=iothread1,drive=drive0 > > Then in the monitor > > snapshot_blkdev drive0 /x/snap1.qcow2 > > qemu bombs with > > qemu-system-x86_64: /x/qemu/include/block/aio.h:457: > aio_enable_external: Assertion `ctx->external_disable_cnt > 0' failed. > > whereas without the iothread the assertion failure does not occur. Please try this patch: diff --git a/block/block-backend.c b/block/block-backend.c index 5742c09..1d95879 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1876,6 +1876,7 @@ static void blk_root_drained_begin(BdrvChild *child) if (blk->public.io_limits_disabled++ == 0) { throttle_group_restart_blk(blk); } + aio_disable_external(bdrv_get_aio_context(bs)); } static void blk_root_drained_end(BdrvChild *child) @@ -1883,5 +1884,6 @@ static void blk_root_drained_end(BdrvChild *child) BlockBackend *blk = child->opaque; assert(blk->public.io_limits_disabled); + aio_enable_external(bdrv_get_aio_context(bs)); --blk->public.io_limits_disabled; } diff --git a/block/io.c b/block/io.c index 2709a70..a6dcef5 100644 --- a/block/io.c +++ b/block/io.c @@ -224,7 +224,6 @@ void bdrv_drained_begin(BlockDriverState *bs) } if (!bs->quiesce_counter++) { - aio_disable_external(bdrv_get_aio_context(bs)); bdrv_parent_drained_begin(bs); } @@ -239,7 +238,6 @@ void bdrv_drained_end(BlockDriverState *bs) } bdrv_parent_drained_end(bs); - aio_enable_external(bdrv_get_aio_context(bs)); } /* This is not a proper fix, the right one would move the calls into virtio-blk and virtio-scsi, but it might be a start. I think the issue is that you have one call to aio_disable_external for drive.qcow2 before the snapshot, and two calls to aio_enable_external (one for drive.qcow2 and one for snap1.qcow2) after. Paolo