linux-kernel - Re: [PATCH 5.15.y] ocfs2: fix deadlock in ocfs2_get_system_file

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Message-ID: <2025071245-snowsuit-pension-061d@gregkh>
Date: Sat, 12 Jul 2025 15:46:00 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Pranav Tyagi <pranav.tyagi03@...il.com>
Cc: ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
	mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com,
	pvmohammedanees2003@...il.com, akpm@...ux-foundation.org,
	sashal@...nel.org, skhan@...uxfoundation.org,
	stable@...r.kernel.org, linux-kernel-mentees@...ts.linux.dev,
	syzbot+e0055ea09f1f5e6fabdd@...kaller.appspotmail.com,
	Junxiao Bi <junxiao.bi@...cle.com>,
	Changwei Ge <gechangwei@...e.cn>, Gang He <ghe@...e.com>,
	Jun Piao <piaojun@...wei.com>
Subject: Re: [PATCH 5.15.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

On Mon, Jun 30, 2025 at 02:05:42PM +0530, Pranav Tyagi wrote:
> From: Mohammed Anees <pvmohammedanees2003@...il.com>
> 
> [ Upstream commit 7bf1823e010e8db2fb649c790bd1b449a75f52d8 ]
> 
> syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].
> 
> The scenario is depicted here,
> 
> 	CPU0					CPU1
> lock(&ocfs2_file_ip_alloc_sem_key);
>                                lock(&osb->system_file_mutex);
>                                lock(&ocfs2_file_ip_alloc_sem_key);
> lock(&osb->system_file_mutex);
> 
> The function calls which could lead to this are:
> 
> CPU0
> ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key);
> .
> .
> .
> ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
> 
> CPU1 -
> ocfs2_fill_super - lock(&osb->system_file_mutex);
> .
> .
> .
> ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);
> 
> This issue can be resolved by making the down_read -> down_read_try
> in the ocfs2_read_virt_blocks.
> 
> [1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
> 
> [ Backport to 5.15: context cleanly applied with no semantic changes.
> Build-tested. ]

We can't take a 5.15.y version, without it being in 6.1.y first, sorry
:(