From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Mon, 18 May 2026 04:23:40 +0000 (+0900)
Subject: ocfs2: kill osb->system_file_mutex lock
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5b1910e23f1233c8d4185268b2e659df2bc5dbf;p=thirdparty%2Fkernel%2Flinux.git

ocfs2: kill osb->system_file_mutex lock

Commit 43b10a20372d ("ocfs2: avoid system inode ref confusion by adding
mutex lock") tried to avoid a refcount leak caused by allowing multiple
threads to call igrab(inode).  But addition of osb->system_file_mutex made
locking dependency complicated and is causing lockdep to warn about
possibility of AB-BA deadlock.

Since _ocfs2_get_system_file_inode() returns the same inode for the same
input arguments, we don't need to serialize
_ocfs2_get_system_file_inode().  What we need to make sure is that
igrab(inode) is called for only once().  Therefore, replace
osb->system_file_mutex with cmpxchg()-based locking.

Link: https://lore.kernel.org/fea8d1fd-afb0-4302-a560-c202e2ef7afd@I-love.SAKURA.ne.jp
Fixes: 43b10a20372d ("ocfs2: avoid system inode ref confusion by adding mutex lock")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Heming Zhao <heming.zhao@suse.com>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index 7b50e03dfa66..62cad6522c7a 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -494,8 +494,6 @@ struct ocfs2_super
 	struct rb_root	osb_rf_lock_tree;
 	struct ocfs2_refcount_tree *osb_ref_tree_lru;
 
-	struct mutex system_file_mutex;
-
 	/*
 	 * OCFS2 needs to schedule several different types of work which
 	 * require cluster locking, disk I/O, recovery waits, etc. Since these
diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index b875f01c9756..6dd45c2153f8 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -1997,8 +1997,6 @@ static int ocfs2_initialize_super(struct super_block *sb,
 	spin_lock_init(&osb->osb_xattr_lock);
 	ocfs2_init_steal_slots(osb);
 
-	mutex_init(&osb->system_file_mutex);
-
 	atomic_set(&osb->alloc_stats.moves, 0);
 	atomic_set(&osb->alloc_stats.local_data, 0);
 	atomic_set(&osb->alloc_stats.bitmap_data, 0);
diff --git a/fs/ocfs2/sysfile.c b/fs/ocfs2/sysfile.c
index d53a6cc866be..67e492f4b828 100644
--- a/fs/ocfs2/sysfile.c
+++ b/fs/ocfs2/sysfile.c
@@ -98,11 +98,9 @@ struct inode *ocfs2_get_system_file_inode(struct ocfs2_super *osb,
 	} else
 		arr = get_local_system_inode(osb, type, slot);
 
-	mutex_lock(&osb->system_file_mutex);
 	if (arr && ((inode = *arr) != NULL)) {
 		/* get a ref in addition to the array ref */
 		inode = igrab(inode);
-		mutex_unlock(&osb->system_file_mutex);
 		BUG_ON(!inode);
 
 		return inode;
@@ -112,11 +110,10 @@ struct inode *ocfs2_get_system_file_inode(struct ocfs2_super *osb,
 	inode = _ocfs2_get_system_file_inode(osb, type, slot);
 
 	/* add one more if putting into array for first time */
-	if (arr && inode) {
-		*arr = igrab(inode);
-		BUG_ON(!*arr);
+	if (inode && arr && !*arr && !cmpxchg(&(*arr), NULL, inode)) {
+		inode = igrab(inode);
+		BUG_ON(!inode);
 	}
-	mutex_unlock(&osb->system_file_mutex);
 	return inode;
 }