From 1e25a392bda9a428ebfa98fe3d6ee11f986983ac Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 19 Nov 2012 08:13:37 -0800
Subject: [PATCH] --- yaml --- r: 339343 b: refs/heads/master c:
 b8a2df6a5b576d04f78f54abf254c283527d8bbc h: refs/heads/master i:   339341:
 7bcfd1d7783a7236b5e312c64cf0e424b76c5a6b   339339:
 05d943288256fd4e947e53227abd390ad71a50ea   339335:
 09f0aa179a503ed0cde20a9eb802f49669646977   339327:
 03f752cf0bbd1a86c612368f05a76eb40cb19f87 v: v3

---
 [refs]                |  2 +-
 trunk/kernel/cgroup.c | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/[refs] b/[refs]
index 2bc4a42b0194..5dd93790f6dc 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: d19e19de48aa0b90c56cd93c8a46ebac46273429
+refs/heads/master: b8a2df6a5b576d04f78f54abf254c283527d8bbc
diff --git a/trunk/kernel/cgroup.c b/trunk/kernel/cgroup.c
index 166b5141f3d4..c53f42e31704 100644
--- a/trunk/kernel/cgroup.c
+++ b/trunk/kernel/cgroup.c
@@ -2657,9 +2657,15 @@ static int cgroup_create_file(struct dentry *dentry, umode_t mode,
 		inc_nlink(inode);
 		inc_nlink(dentry->d_parent->d_inode);
 
-		/* start with the directory inode held, so that we can
-		 * populate it without racing with another mkdir */
-		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+		/*
+		 * Control reaches here with cgroup_mutex held.
+		 * @inode->i_mutex should nest outside cgroup_mutex but we
+		 * want to populate it immediately without releasing
+		 * cgroup_mutex.  As @inode isn't visible to anyone else
+		 * yet, trylock will always succeed without affecting
+		 * lockdep checks.
+		 */
+		WARN_ON_ONCE(!mutex_trylock(&inode->i_mutex));
 	} else if (S_ISREG(mode)) {
 		inode->i_size = 0;
 		inode->i_fop = &cgroup_file_operations;