FAILED: patch "[PATCH] Btrfs: fix deadlock between clone/dedupe and rename" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4ea748e1d2c9f8a27332b949e8210dbbf392987e Mon Sep 17 00:00:00 2001
From: Filipe Manana <[email protected]>
Date: Tue, 26 Feb 2019 12:06:09 +0000
Subject: [PATCH] Btrfs: fix deadlock between clone/dedupe and rename

Reflinking (clone/dedupe) and rename are operations that operate on two inodes and therefore need to lock them in the same order to avoid ABBA deadlocks. It happens that Btrfs' reflink implementation always locked them in a different order from VFS's lock_two_nondirectories() helper, which is used by the rename code in VFS, resulting in ABBA type deadlocks.

Btrfs' locking order:

  static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
  {
         if (inode1 < inode2)
                swap(inode1, inode2);

         inode_lock_nested(inode1, I_MUTEX_PARENT);
         inode_lock_nested(inode2, I_MUTEX_CHILD);

}

VFS's locking order:

  void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
  {
        if (inode1 > inode2)
                swap(inode1, inode2);

        if (inode1 && !S_ISDIR(inode1->i_mode))
                inode_lock(inode1);
        if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
                inode_lock_nested(inode2, I_MUTEX_NONDIR2);
}

Fix this by killing the btrfs helper function that does the double inode locking and replace it with VFS's helper lock_two_nondirectories().

index 494f0f10d70e..ec2d8919e7fb 100644
@@ -3207,21 +3207,6 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
-static void btrfs_double_inode_unlock(struct inode *inode1, struct inode *inode2)
-{
-	inode_unlock(inode1);
-	inode_unlock(inode2);
-}
-
-static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
-{
-	if (inode1 < inode2)
-		swap(inode1, inode2);
-
-	inode_lock_nested(inode1, I_MUTEX_PARENT);
-	inode_lock_nested(inode2, I_MUTEX_CHILD);
-}
-
 static void btrfs_double_extent_unlock(struct inode *inode1, u64 loff1,
 				       struct inode *inode2, u64 loff2, u64 len)
 {

@@ -3956,7 +3941,7 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	if (same_inode)
 		inode_lock(inode_in);
 	else
-		btrfs_double_inode_lock(inode_in, inode_out);
+		lock_two_nondirectories(inode_in, inode_out);
 
 	/* don't make the dst file partly checksummed */
 	if ((BTRFS_I(inode_in)->flags & BTRFS_INODE_NODATASUM) !=

@@ -4013,7 +3998,7 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	if (same_inode)
 		inode_unlock(inode_in);
 	else
-		btrfs_double_inode_unlock(inode_in, inode_out);
+		unlock_two_nondirectories(inode_in, inode_out);
 
 	return ret;
 }

@@ -4043,7 +4028,7 @@ loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
 	if (same_inode)
 		inode_unlock(src_inode);
 	else
-		btrfs_double_inode_unlock(src_inode, dst_inode);
+		unlock_two_nondirectories(src_inode, dst_inode);
 
 	return ret < 0 ? ret : len;
 }