Re: [Qemu-devel] [PATCH v2 1/6] block: avoid recursive AioContext acquire in bdrv_inactivate_all()

[Eric Blake <eblake@redhat.com>]

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On 12/07/2017 02:13 PM, Stefan Hajnoczi wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> BDRV_POLL_WHILE() does not support recursive AioContext locking.  It
> only releases the AioContext lock once regardless of how many times the
> caller has acquired it.  This results in a hang since the IOThread does
> not make progress while the AioContext is still locked.
> 
> The following steps trigger the hang:
> 
>   $ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
>                        -object iothread,id=iothread0 \
>                        -device virtio-scsi-pci,iothread=iothread0 \
>                        -drive if=none,id=drive0,file=test.img,format=raw \
>                        -device scsi-hd,drive=drive0 \
>                        -drive if=none,id=drive1,file=test.img,format=raw \
>                        -device scsi-hd,drive=drive1
>   $ qemu-system-x86_64 ...same options... \
>                        -incoming tcp::1234
>   (qemu) migrate tcp:127.0.0.1:1234
>   ...hang...
> 
> Tested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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