Btrfs: allow file data clone within a file

We did not allow file data clone within the same file because of
deadlock issues.

However, we now use nested lock to avoid deadlock between the
parent directory and the child file.

So it's safe to do file clone within the same file when the two
ranges are not overlapped.
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ioctl.c

@@ -2486,6 +2486,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	int ret;
 	u64 len = olen;
 	u64 bs = root->fs_info->sb->s_blocksize;
+	int same_inode = 0;
 
 	/*
 	 * TODO:
@@ -2522,7 +2523,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
 	ret = -EINVAL;
 	if (src == inode)
-		goto out_fput;
+		same_inode = 1;
 
 	/* the src must be open for reading */
 	if (!(src_file.file->f_mode & FMODE_READ))
@@ -2553,12 +2554,16 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	}
 	path->reada = 2;
 
-	if (inode < src) {
-		mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
-		mutex_lock_nested(&src->i_mutex, I_MUTEX_CHILD);
+	if (!same_inode) {
+		if (inode < src) {
+			mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
+			mutex_lock_nested(&src->i_mutex, I_MUTEX_CHILD);
+		} else {
+			mutex_lock_nested(&src->i_mutex, I_MUTEX_PARENT);
+			mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+		}
 	} else {
-		mutex_lock_nested(&src->i_mutex, I_MUTEX_PARENT);
-		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+		mutex_lock(&src->i_mutex);
 	}
 
 	/* determine range to clone */
@@ -2576,6 +2581,12 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	    !IS_ALIGNED(destoff, bs))
 		goto out_unlock;
 
+	/* verify if ranges are overlapped within the same file */
+	if (same_inode) {
+		if (destoff + len > off && destoff < off + len)
+			goto out_unlock;
+	}
+
 	if (destoff > inode->i_size) {
 		ret = btrfs_cont_expand(inode, inode->i_size, destoff);
 		if (ret)
@@ -2852,7 +2863,8 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	unlock_extent(&BTRFS_I(src)->io_tree, off, off + len - 1);
 out_unlock:
 	mutex_unlock(&src->i_mutex);
-	mutex_unlock(&inode->i_mutex);
+	if (!same_inode)
+		mutex_unlock(&inode->i_mutex);
 	vfree(buf);
 	btrfs_free_path(path);
 out_fput: