Re: [Qemu-devel] Block Migration Assertion in qemu-kvm 1.2.0

[Kevin Wolf <kwolf@redhat.com>]

Am 19.09.2012 07:49, schrieb Peter Lieven:
> On 09/18/12 12:31, Kevin Wolf wrote:
>> Am 18.09.2012 12:28, schrieb Peter Lieven:
>>> On 09/17/12 22:12, Peter Lieven wrote:
>>>> On 09/17/12 10:41, Kevin Wolf wrote:
>>>>> Am 16.09.2012 12:13, schrieb Peter Lieven:
>>>>>> Hi,
>>>>>>
>>>>>> when trying to block migrate a VM from one node to another, the source
>>>>>> VM crashed with the following assertion:
>>>>>> block.c:3829: bdrv_set_in_use: Assertion `bs->in_use != in_use' failed.
>>>>>>
>>>>>> Is this sth already addresses/known?
>>>>> Not that I'm aware of, at least.
>>>>>
>>>>> Block migration doesn't seem to check whether the device is already in
>>>>> use, maybe this is the problem. Not sure why it would be in use, though,
>>>>> and in my quick test it didn't crash.
>>>>>
>>>>> So we need some more information: What's you command line, did you do
>>>>> anything specific in the monitor with block devices, what does the
>>>>> stacktrace look like, etc.?
>>>> kevin, it seems that i can very easily force a crash if I cancel a
>>>> running block migration.
>>> if I understand correctly what happens there are aio callbacks coming in
>>> after
>>> blk_mig_cleanup() has been called.
>>>
>>> what is the proper way to detect this in blk_mig_read_cb()?
>> You could try this, it doesn't detect the situation in
>> blk_mig_read_cb(), but ensures that all callbacks happen before we do
>> the actual cleanup (completely untested):
> after testing it for half an hour i can say, it seems to fix the problem.
> no segfaults and also no other assertions.
> 
> while searching I have seen that the queses blk_list and bmds_list are 
> initialized at
> qemu startup. wouldn't it be better to initialize them at init_blk_migration
> or at least check that they are really empty? i have also seen that 
> prev_time_offset
> is not initialized.

Probably. If you sent this as a proper patch with a SoB, I wouldn't
reject it, but considering that block migration is deprecated anyway, I
won't bother myself as long as there's no real bug.

Kevin