Re: [Qemu-devel] [PATCH 1/9] blockdev: hold AioContext for bdrv_unref() in external_snapshot_clean()

[Eric Blake <eblake@redhat.com>]

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On 12/05/2017 04:41 AM, Stefan Hajnoczi wrote:
> bdrv_unref() requires the AioContext lock because bdrv_flush() uses
> BDRV_POLL_WHILE(), which assumes the AioContext is currently held.  If
> BDRV_POLL_WHILE() runs without AioContext held the
> pthread_mutex_unlock() call in aio_context_release() fails.
> 
> This patch moves bdrv_unref() into the AioContext locked region to solve
> the following pthread_mutex_unlock() failure:
> 
>   #0  0x00007f566181969b in raise () at /lib64/libc.so.6
>   #1  0x00007f566181b3b1 in abort () at /lib64/libc.so.6
>   #2  0x00005592cd590458 in error_exit (err=<optimized out>, msg=msg@entry=0x5592cdaf6d60 <__func__.23977> "qemu_mutex_unlock") at util/qemu-thread-posix.c:36
>   #3  0x00005592cd96e738 in qemu_mutex_unlock (mutex=mutex@entry=0x5592ce9505e0) at util/qemu-thread-posix.c:96
>   #4  0x00005592cd969b69 in aio_context_release (ctx=ctx@entry=0x5592ce950580) at util/async.c:507
>   #5  0x00005592cd8ead78 in bdrv_flush (bs=bs@entry=0x5592cfa87210) at block/io.c:2478
>   #6  0x00005592cd89df30 in bdrv_close (bs=0x5592cfa87210) at block.c:3207
>   #7  0x00005592cd89df30 in bdrv_delete (bs=0x5592cfa87210) at block.c:3395
>   #8  0x00005592cd89df30 in bdrv_unref (bs=0x5592cfa87210) at block.c:4418
>   #9  0x00005592cd6b7f86 in qmp_transaction (dev_list=<optimized out>, has_props=<optimized out>, props=<optimized out>, errp=errp@entry=0x7ffe4a1fc9d8) at blockdev.c:2308
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  blockdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

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

I know the series is too big/late for 2.11, but is this one patch worth
having?

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


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