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

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Message-ID: <CAH4c4jKMvLhgT_-2z_LH9scGQbT3J2tgH-RUXAUJ-5c30251MA@mail.gmail.com>
Date: Sat, 12 Jul 2025 22:41:50 +0530
From: Pranav Tyagi <pranav.tyagi03@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
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 Sat, Jul 12, 2025 at 7:16 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> 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
> :(
>

Hi,

Thanks for pointing that out. I wasn’t aware of the 6.1.y prerequisite
for 5.15.y backports. Learned something new today. I’ll make sure to get
it into 6.1.y first.

Regards
Pranav Tyagi