Re: [bug report] BUG: kernel NULL pointer dereference, address: 0000000000000048

[Yu Kuai <yukuai1@huaweicloud.com>]

Hi, Jens

在 2023/05/10 10:17, Jens Axboe 写道:
> On 5/9/23 8:00?PM, Yu Kuai wrote:
>> Hi,
>>
>> ? 2023/05/10 9:49, Yu Kuai ??:
>>> Hi,
>>>
>>> ? 2023/05/10 9:29, Yu Kuai ??:
>>>> Hi,
>>>>
>>>> ? 2023/05/10 8:49, Guangwu Zhang ??:
>>>>> Hi,
>>>>>
>>>>> We found this kernel NULL pointer issue with latest
>>>>> linux-block/for-next, please check it.
>>>>>
>>>>> Kernel repo: https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
>>>>>
>>>>>
>>>>> [  112.483804] BUG: kernel NULL pointer dereference, address: 0000000000000048
>>>
>>> Base on this offset, 0x48 match bio->bi_blkg, so I guess this is because
>>> bio is NULL, so the problem is that passthrough request insert into
>>> elevator.
>>>
>> Sorry that attached patch has some problem, please try this one.
> 
> Let's please fix this in bfq, this isn't a core issue and it's not a
> good idea to work around it there.
> 

I can do that, but I'm not sure because it seems passthrough rq is not
supposed to insert into elevator.

Bfq always expect that bio is not NULL, and before this commit
a327c341dc65 ("blk-mq: fix passthrough plugging"), passthrough rq can
never insert into plug, and therefor passthrough rq can never insert
into elevator.

Thanks,
Kuai