linux-kernel - Re: linux-next: BUG: unable to handle kernel NULL pointer dereference in cfq_print_leaf

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Date:	Mon, 22 Jun 2015 23:13:28 +0300
From:	Andrey Wagin <avagin@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Arianna Avanzini <avanzini.arianna@...il.com>
Subject: Re: linux-next: BUG: unable to handle kernel NULL pointer dereference
 in cfq_print_leaf_weight()

2015-06-19 23:26 GMT+03:00 Andrey Wagin <avagin@...il.com>:
> 2015-06-19 19:24 GMT+03:00 Jens Axboe <axboe@...nel.dk>:
>> On 06/17/2015 03:55 PM, Andrey Wagin wrote:
>>>
>>> Hi All,
>>>
>>> I executed CRIU tests on the 4.1.0-rc8-next-20150617 kernel and met
>>> this bug. Maybe it will be interested for someone to look at it.
>>
>>
>> This should fix it:
>>
>> http://git.kernel.dk/cgit/linux-block/commit/?h=for-4.2/core&id=9470e4a693db84bee7becbba8de01af02bb23c9f
>
> Hi Jens,
>
> Thank you for the path. I think we need to fix __cfq_set_weight and
> __cfq_set_weight_device too.

I've seen that you fixed these functions too. But CRIU tests still
fail, because they tries to restore a value of blkio.weight and get
EINVAL. It works fine on the upstream kernel.

For me the suggested interface looks weird. What if a device which
uses cfq isn't permanent. If I detach the device, cgroup configuration
will be destroyed and then if I attach the device again, I will need
to apply cgroup parameters again.

Thanks,
Andrew
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