linux-kernel - Re: [PATCH v2] md/raid1: Fix stack memory use after return in raid1

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Message-ID: <9275145b-3066-41e5-a971-eba219ef0d3c@gmail.com>
Date: Thu, 12 Jun 2025 20:21:51 +0800
From: Wang Jinchao <wangjinchao600@...il.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Song Liu <song@...nel.org>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2] md/raid1: Fix stack memory use after return in
 raid1_reshape

On 2025/6/12 19:58, Yu Kuai wrote:
> Hi,
> 
> 在 2025/06/12 19:46, Wang Jinchao 写道:
>> On 2025/6/12 19:23, Yu Kuai wrote:
>>> Hi,
>>>
>>> 在 2025/06/12 17:55, Wang Jinchao 写道:
>>>> Now that we have the same information, I prefer patch-v1 before 
>>>> refactoring raid1_reshape,
>>>> because it’s really simple (only one line) and clearer to show the 
>>>> backup and restore logic.
>>>> Another reason is that v2 freezes the RAID longer than v1.
>>>> Would you like me to provide a v3 patch combining the v2 explanation 
>>>> with the v1 diff?
>>>> Thanks for your reviewing.
>>>
>>> I don't have preference here, feel free to do this.
>>>
>>> BTW, I feel raid1_reshape can be better coding with following：
>>>
>>> - covert r1bio_pool to use mempool_create_kmalloc_pool(use create
>>> instead of init to get rid of the werid assigment);
>> mempool_create_kmalloc_pool also calls init_waitqueue_head(&pool- 
>> >wait) internally, just like mempool_init.
> 
> Please notice that creat will allocate memory for mempool, the list is
> no longer a stack value, the field bio_pool inside conf should also
> covert to a pointer.
> 
>> So the issue only exists if newpool is allocated on the stack.
>>> - no need to reallocate pool_info;
>>> - convert raid1_info to use krealloc;
>> I think reallocating pool_info is only for backup and restore, similar 
>> to newpool.
> 
> You can just change the old value directly, after everything is ready,
> with the first mempool change, pool_info is not needed for bio_pool.
>>>
>>> Welcome if you are willing to, otherwise I'll find myself sometime.
>> I'm a newcomer to RAID and can't quite catch up with it right now.
>> Maybe I can refactor it later, and I look forward to your guidance.
>>>
> 
> No hurry, take you time :)
👍
You're right — now I understand the whole.
I'm willing to try refactoring raid1_reshape later.
> 
> Thanks,
> Kuai
>