On 19/01/2016 23:02, Roman Mamedov wrote: > Hello, > > I'm facing a strange issue: > > Starting with the kernel 4.4.0, a KVM guest stored on a Btrfs > filesystem, if it's using the "virtio-scsi" disk backend, will hard > lock-up instantly, as soon as the Btrfs subvolume which contains > its backing file is snapshotted. So this is kernel 4.4 on the host, and virtio-scsi in the guest. What about virtio-blk in the guest? The only difference I can see between ide and virtio-* is that IDE only has a queue depth of 1. > There's nothing in dmesg neither on the guest, nor on the host; the > KVM process can be killed from the host just fine and then > restarted, so it doesn't seem to be a kernel-side deadlock of any > sort. > > KVM disk controller which exhibits the problem: > > -device virtio-scsi-pci,id=scsi -device scsi-hd,drive=hd \ > > The alternative which works fine: > > -device ide-hd,drive=hd,bus=ide.0 \ > > The disk device line is common to both cases: > > -drive > if=none,id=hd,cache=writeback,aio=threads,format=raw,file=$NAME.img,discard=unmap,detect-zeroes=unmap > \ So you're snapshotting the subvolume that includes $NAME.img? Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
