quoted

It's safe and easy to do so, provided the ranges don't overlap.

Signed-off-by: Li Zefan <redacted>
---
 fs/btrfs/ioctl.c |   23 ++++++++++++++++-------
 1 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0b06a5c..8fcd671 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c

@@ -2223,8 +2223,6 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	 *   decompress into destination's address_space (the file offset
 	 *   may change, so source mapping won't do), then recompress (or
 	 *   otherwise reinsert) a subrange.
-	 * - allow ranges within the same file to be cloned (provided
-	 *   they don't overlap)?
 	 */
 
 	/* the destination must be opened for writing */

@@ -2247,8 +2245,6 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	src = src_file->f_dentry->d_inode;
 
 	ret = -EINVAL;
-	if (src == inode)
-		goto out_fput;
 
 	/* the src must be open for reading */
 	if (!(src_file->f_mode & FMODE_READ))

@@ -2282,9 +2278,11 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	if (inode < src) {
 		mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
 		mutex_lock_nested(&src->i_mutex, I_MUTEX_CHILD);
-	} else {
+	} else if (inode > src) {
 		mutex_lock_nested(&src->i_mutex, I_MUTEX_PARENT);
 		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+	} else {
+		mutex_lock(&inode->i_mutex);
 	}
 
 	/* determine range to clone */

@@ -2302,6 +2300,13 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	    !IS_ALIGNED(destoff, bs))
 		goto out_unlock;
 
+	/*
+	 * allow ranges within the same file to be cloned only if
+	 * they don't overlap
+	 */
+	if (src == inode && !(off + len <= destoff || destoff + len <= off))

            ^^^^^^^^^^^^
... this check isn't sufficient. Two different inodes can reference the
same data extent and we must prevent overlap cloning there as well.

Could you be more elaborate on this? I don't know what's the problem
you're refering to.