linux-kernel - Re: [PATCH] mm: list_lru: Fix NULL pointer dereference in list_lru

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Message-ID: <56a81429-4e1e-46f9-8844-acb1afd66952@bytedance.com>
Date: Mon, 15 Jul 2024 11:27:18 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Youling Tang <youling.tang@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Youling Tang <tangyouling@...inos.cn>
Subject: Re: [PATCH] mm: list_lru: Fix NULL pointer dereference in
 list_lru_add()



On 2024/7/12 12:07, Kent Overstreet wrote:
> On Fri, Jul 12, 2024 at 11:25:54AM GMT, Youling Tang wrote:
>> From: Youling Tang <tangyouling@...inos.cn>
>>
>> Note that list_lru_from_memcg_idx() may return NULL, so it is necessary
>> to error handle the return value to avoid triggering NULL pointer
>> dereference BUG.
>>
>> The issue was triggered for discussion [1],
>> Link [1]: https://lore.kernel.org/linux-bcachefs/84de6cb1-57bd-42f7-8029-4203820ef0b4@linux.dev/T/#m901bb26cdb1d9d4bacebf0d034f0a5a712cc93a6
> 
> I see no explanation for why this is the correct fix, and I doubt it is.
> What's the real reason for the NULL lru_list_one, and why doesn't this
> come up on other filesystems?

Agree, IIRC, the list_lru_one will be pre-allocated in the allocation
path of inode/dentry etc.