Re: [Qemu-devel] [PATCH] vl.c/exit: pause cpus before closing block devices

[Paolo Bonzini]

On 04/08/2017 11:58, Stefan Hajnoczi wrote:
>> the root cause of this bug is related to this as well:
>> https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg02945.html
>>
>> From commit 99723548 we started assuming (incorrectly?) that blk_
>> functions always WILL have an attached BDS, but this is not always true,
>> for instance, flushing the cache from an empty CDROM.
>>
>> Paolo, can we move the flight counter increment outside of the
>> block-backend layer, is that safe?
> I think the bdrv_inc_in_flight(blk_bs(blk)) needs to be fixed
> regardless of the throttling timer issue discussed below.  BB cannot
> assume that the BDS graph is non-empty.

Can we make bdrv_aio_* return NULL (even temporarily) if there is no
attached BDS?  That would make it much easier to fix.

Paolo