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Re: [Qemu-devel] Assertion failure taking external snapshot with virtio
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread |
Date: |
Fri, 17 Mar 2017 18:11:35 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
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
- [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Ed Swierk, 2017/03/17
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread,
Paolo Bonzini <=
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Paolo Bonzini, 2017/03/17
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Ed Swierk, 2017/03/17
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Paolo Bonzini, 2017/03/17
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Paolo Bonzini, 2017/03/17
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Ed Swierk, 2017/03/20
- Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Ed Swierk, 2017/03/20
Re: [Qemu-devel] Assertion failure taking external snapshot with virtio drive + iothread, Fam Zheng, 2017/03/21