On 17/03/2017 18:32, Ed Swierk wrote: > On Fri, Mar 17, 2017 at 10:15 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: >> >> >> On 17/03/2017 18:11, Paolo Bonzini wrote: >>> >>> >>> 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: >> >> Hmm, no. I'll post the full fix on top of John Snow's patches. > > OK. Incidentally, testing with virtio-blk I bisected the assertion > failure to b2c2832c6140cfe3ddc0de2d77eeb0b77dea8fd3 ("block: Add Error > parameter to bdrv_append()").
And in particular to this: + bdrv_set_backing_hd(bs_new, bs_top, &local_err); + if (local_err) { + error_propagate(errp, local_err); + goto out; + } change_parent_backing_link(bs_top, bs_new); - /* FIXME Error handling */ - bdrv_set_backing_hd(bs_new, bs_top, &error_abort); Paolo