Patch "Btrfs: fix lockdep warning about log_mutex" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

Btrfs: fix lockdep warning about log_mutex

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-lockdep-warning-about-log_mutex.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Liu Bo <[email protected]>
Date: Wed, 30 Nov 2016 16:20:25 -0800
Subject: Btrfs: fix lockdep warning about log_mutex

From: Liu Bo <[email protected]>

[ Upstream commit 781feef7e6befafd4d9787d1f7ada1f9ccd504e4 ]

While checking INODE_REF/INODE_EXTREF for a corner case, we may acquire a different inode's log_mutex with holding the current inode's log_mutex, and lockdep has complained this with a possilble deadlock warning.

Fix this by using mutex_lock_nested() when processing the other inode's log_mutex.

---
 fs/btrfs/tree-log.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

@@ -37,6 +37,7 @@
  */
 #define LOG_INODE_ALL 0
 #define LOG_INODE_EXISTS 1
+#define LOG_OTHER_INODE 2
 
 /*
  * directory trouble cases

@@ -4623,7 +4624,7 @@ static int btrfs_log_inode(struct btrfs_
 	if (S_ISDIR(inode->i_mode) ||
 	    (!test_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
 		       &BTRFS_I(inode)->runtime_flags) &&
-	     inode_only == LOG_INODE_EXISTS))
+	     inode_only >= LOG_INODE_EXISTS))
 		max_key.type = BTRFS_XATTR_ITEM_KEY;
 	else
 		max_key.type = (u8)-1;

@@ -4647,7 +4648,13 @@ static int btrfs_log_inode(struct btrfs_
 		return ret;
 	}
 
-	mutex_lock(&BTRFS_I(inode)->log_mutex);
+	if (inode_only == LOG_OTHER_INODE) {
+		inode_only = LOG_INODE_EXISTS;
+		mutex_lock_nested(&BTRFS_I(inode)->log_mutex,
+				  SINGLE_DEPTH_NESTING);
+	} else {
+		mutex_lock(&BTRFS_I(inode)->log_mutex);
+	}
 
 	/*
 	 * a brute force approach to making sure we get the most uptodate

@@ -4799,7 +4806,7 @@ again:
 				 * unpin it.
 				 */
 				err = btrfs_log_inode(trans, root, other_inode,
-						      LOG_INODE_EXISTS,
+						      LOG_OTHER_INODE,
 						      0, LLONG_MAX, ctx);
 				iput(other_inode);
 				if (err)

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/btrfs-fix-lockdep-warning-about-log_mutex.patch queue-4.9/btrfs-adjust-outstanding_extents-counter-properly-when-dio-write-is-split.patch queue-4.9/btrfs-use-down_read_nested-to-make-lockdep-silent.patch