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

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Message-ID: <CALW65jbQCvkpeoOv275jgQAHf+Tk3QBR0HdwdGhK3s7gF+HVeg@mail.gmail.com>
Date: Tue, 19 Mar 2024 14:41:59 +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

On Fri, Mar 15, 2024 at 9:00 PM Zhihao Cheng <chengzhihao1@...wei.com> wrote:
>
> 在 2024/3/15 20:19, Qingfang Deng 写道:
> > 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.
> > .
> >
> Allocating memory without GFP_NOFS flags under sleeping lock is a normal
> thing. The vfs_write is an example(eg. ext4), page is allocated with
> FGP_WRITEBEGIN flag(no FGP_NOFS) when holding inode lock.

If this is a false positive, is there a way to suppress the warning?