Re: [Qemu-devel] [PATCH] throttle: Fix crash on reopen

[Max Reitz <mreitz@redhat.com>]

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On 2018-06-08 17:15, Alberto Garcia wrote:
> The throttle block filter can be reopened, and with this it is
> possible to change the throttle group that the filter belongs to.
> 
> The way the code does that is the following:
> 
>   - On throttle_reopen_prepare(): create a new ThrottleGroupMember
>     and attach it to the new throttle group.
> 
>   - On throttle_reopen_commit(): detach the old ThrottleGroupMember,
>     delete it and replace it with the new one.
> 
> The problem with this is that by replacing the ThrottleGroupMember the
> previous value of io_limits_disabled is lost, causing an assertion
> failure in throttle_co_drain_end().
> 
> This problem can be reproduced by reopening a throttle node:
> 
>    $QEMU -monitor stdio
>    -object throttle-group,id=tg0,x-iops-total=1000 \
>    -blockdev node-name=hd0,driver=qcow2,file.driver=file,file.filename=hd.qcow2 \
>    -blockdev node-name=root,driver=throttle,throttle-group=tg0,file=hd0,read-only=on
> 
>    (qemu) block_stream root
>    block/throttle.c:214: throttle_co_drain_end: Assertion `tgm->io_limits_disabled' failed.
> 
> Since we only want to change the throttle group on reopen there's no
> need to create a ThrottleGroupMember and discard the old one. It's
> easier if we simply detach it from its current group and attach it to
> the new one.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/throttle.c | 54 +++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 33 insertions(+), 21 deletions(-)

Thanks, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max


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