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

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Message-ID: <sd32qchit33aafht27utinrz5dizw62qbtwdmwbtugqrlglmtx@6aitsotgqnpi>
Date: Fri, 12 Jul 2024 00:07:32 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Youling Tang <youling.tang@...ux.dev>
Cc: 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 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?