Re: Unable to handle kernel NULL pointer dereference in super_written

[Shaohua Li <shlikernel@gmail.com>]

On 03/29/2016 07:34 PM, Guoqing Jiang wrote:
>
>
> On 03/30/2016 05:37 AM, Shaohua Li wrote:
>> On Tue, Mar 29, 2016 at 08:22:00AM -0400, Xiao Ni wrote:
>>> Hi all
>>>
>>> I encountered one NULL pointer dereference problem.
>>>
>>> The environment：
>>> latest linux-stable and mdadm codes
>>> aarch64 platform
>>> the md device is created with loop devices
>>>
>>> It's a test case to check date integrity. I added the test script as 
>>> the attachment.
>> Could you please try this patch:
>>
>>
>>  From b86d9e1724184c79ad1ea63901aec802492b861c Mon Sep 17 00:00:00 2001
>> Message-Id: 
>> <b86d9e1724184c79ad1ea63901aec802492b861c.1459285706.git.shli@fb.com>
>> From: Shaohua Li <shli@fb.com>
>> Date: Tue, 29 Mar 2016 14:00:19 -0700
>> Subject: [PATCH] MD: add rdev reference for super write
>>
>> md_super_write() and corresponding md_super_wait() generally are called
>> with reconfig_mutex locked, which prevents disk disappears.
>
> Just for curious, I find several paths maybe also don't hold 
> reconfig_mutex,
> take the followings as example.
>
> 1.  md_run -> md_update_sb -> md_super_write/md_super_wait
> 2.  rdev_size_store -> rdev_size_change -> md_super_write/md_super_wait
we do mddev_lock/unlock calling these. The rdev_size_sotre is a bit 
tricky. the lock is hold in rdev_attr_store

Thanks,
Shaohua
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