From: Paolo Bonzini <pbonzini@redhat.com>
To: Roman Mamedov <rm@romanrm.net>,
linux-btrfs@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: Kernel 4.4.0 KVM guest on Btrfs locks up on snapshotting
Date: Tue, 19 Jan 2016 23:18:59 +0100 [thread overview]
Message-ID: <569EB653.9080700@redhat.com> (raw)
In-Reply-To: <20160120030223.22cc3ae0@natsu>
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
next prev parent reply other threads:[~2016-01-19 22:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-19 22:02 Kernel 4.4.0 KVM guest on Btrfs locks up on snapshotting Roman Mamedov
2016-01-19 22:18 ` Paolo Bonzini [this message]
2016-01-19 23:03 ` Roman Mamedov
2016-01-20 8:28 ` Paolo Bonzini
2016-01-20 13:58 ` Roman Mamedov
2016-01-20 17:28 ` Paolo Bonzini
2016-01-20 18:46 ` Roman Mamedov
2016-01-20 20:38 ` Paolo Bonzini
2016-01-20 0:19 ` Liu Bo
2016-01-20 5:08 ` Roman Mamedov
2016-01-20 11:34 ` Paolo Bonzini
2016-01-20 15:08 ` Roman Mamedov
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