linux-kernel - Re: [RFC PATCH] jffs2: fix recursive fs

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Date: Fri, 15 Mar 2024 20:19:30 +0800
From: Qingfang Deng <dqfext@...il.com>
To: Zhihao Cheng <chengzhihao1@...wei.com>
Cc: David Woodhouse <dwmw2@...radead.org>, Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] jffs2: fix recursive fs_reclaim deadlock

Hi Zhihao,

On Fri, Mar 15, 2024 at 7:19 PM Zhihao Cheng <chengzhihao1@...wei.com> wrote:
> I think it's a false positive warning. Jffs2 is trying to get root inode
> in process '#1', which means that the filesystem is not mounted
> yet(Because d_make_root is after jffs2_iget(sb,1), there is no way to
> access other inodes.), so it is impossible that jffs2 inode is being
> evicted in '#0'.
>

You're right that process '#1' is getting the root inode. However,
lockdep only records the stack of the first unique lock ordering (see
https://docs.kernel.org/locking/lockdep-design.html#performance ), and
there are many occasions where GFP_KERNEL is used inside a
jffs2_inode_info::sem 's critical section.