linux-kernel - [PATCH 6.6 2/2] nilfs2: fix deadlock warnings caused by lock dependency in init

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Message-ID: <20251020122541.7227-2-mngyadam@amazon.de>
Date: Mon, 20 Oct 2025 14:25:39 +0200
From: Mahmoud Adam <mngyadam@...zon.de>
To: <stable@...r.kernel.org>
CC: <gregkh@...uxfoundation.org>, <nagy@...aternagy.com>, Ryusuke Konishi
	<konishi.ryusuke@...il.com>,
	<syzbot+00f7f5b884b117ee6773@...kaller.appspotmail.com>,
	<syzbot+f30591e72bfc24d4715b@...kaller.appspotmail.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Luis Chamberlain
	<mcgrof@...nel.org>, "Darrick J. Wong" <djwong@...nel.org>,
	<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-nilfs@...r.kernel.org>
Subject: [PATCH 6.6 2/2] nilfs2: fix deadlock warnings caused by lock dependency in init_nilfs()

From: Ryusuke Konishi <konishi.ryusuke@...il.com>

commit fb881cd7604536b17a1927fb0533f9a6982ffcc5 upstream.

After commit c0e473a0d226 ("block: fix race between set_blocksize and read
paths") was merged, set_blocksize() called by sb_set_blocksize() now locks
the inode of the backing device file.  As a result of this change, syzbot
started reporting deadlock warnings due to a circular dependency involving
the semaphore "ns_sem" of the nilfs object, the inode lock of the backing
device file, and the locks that this inode lock is transitively dependent
on.

This is caused by a new lock dependency added by the above change, since
init_nilfs() calls sb_set_blocksize() in the lock section of "ns_sem".
However, these warnings are false positives because init_nilfs() is called
in the early stage of the mount operation and the filesystem has not yet
started.

The reason why "ns_sem" is locked in init_nilfs() was to avoid a race
condition in nilfs_fill_super() caused by sharing a nilfs object among
multiple filesystem instances (super block structures) in the early
implementation.  However, nilfs objects and super block structures have
long ago become one-to-one, and there is no longer any need to use the
semaphore there.

So, fix this issue by removing the use of the semaphore "ns_sem" in
init_nilfs().

Link: https://lkml.kernel.org/r/20250503053327.12294-1-konishi.ryusuke@gmail.com
Fixes: c0e473a0d226 ("block: fix race between set_blocksize and read paths")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
Reported-by: syzbot+00f7f5b884b117ee6773@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=00f7f5b884b117ee6773
Tested-by: syzbot+00f7f5b884b117ee6773@...kaller.appspotmail.com
Reported-by: syzbot+f30591e72bfc24d4715b@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f30591e72bfc24d4715b
Tested-by: syzbot+f30591e72bfc24d4715b@...kaller.appspotmail.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Mahmoud Adam <mngyadam@...zon.de>
---
    Follow up fix.

 fs/nilfs2/the_nilfs.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index be41e26b782469..05fdbbc63e1f5f 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -680,8 +680,6 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
 	int blocksize;
 	int err;

-	down_write(&nilfs->ns_sem);
-
 	blocksize = sb_min_blocksize(sb, NILFS_MIN_BLOCK_SIZE);
 	if (!blocksize) {
 		nilfs_err(sb, "unable to set blocksize");
@@ -757,7 +755,6 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
 	set_nilfs_init(nilfs);
 	err = 0;
  out:
-	up_write(&nilfs->ns_sem);
 	return err;

  failed_sbh:
-- 
2.47.3

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