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. 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 \ Also tried aio=native with the problematic variant, no change. Both variants work fine and unaffected by snapshotting on kernel 3.18.25. Any ideas? -- With respect, Roman
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