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.

Signed-off-by: Liu Bo <bo.li....@oracle.com>
---
 fs/btrfs/tree-log.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 3d33c4e..e961451 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -37,6 +37,7 @@
  */
 #define LOG_INODE_ALL 0
 #define LOG_INODE_EXISTS 1
+#define LOG_OTHER_INODE 2
 
 /*
  * directory trouble cases
@@ -4624,7 +4625,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle 
*trans,
        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;
@@ -4648,7 +4649,12 @@ static int btrfs_log_inode(struct btrfs_trans_handle 
*trans,
                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, 1);
+       } else {
+               mutex_lock(&BTRFS_I(inode)->log_mutex);
+       }
 
        /*
         * a brute force approach to making sure we get the most uptodate
@@ -4800,7 +4806,7 @@ static int btrfs_log_inode(struct btrfs_trans_handle 
*trans,
                                 * 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)
-- 
2.5.5

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