Merge tag 'fs-dedupe-last-block-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

Pull fs deduplication fix from David Sterba:
 "This is a fix for deduplication bug: the last block of two files is
  allowed to deduplicated. This got broken in 5.1 by lifting some
  generic checks to VFS layer. The affected filesystems are btrfs and
  xfs.

  The patches are marked for stable as the bug decreases deduplication
  effectivity"

* tag 'fs-dedupe-last-block-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
  Btrfs: make deduplication with range including the last block work
  fs: allow deduplication of eof block into the end of the destination file

fs/btrfs/ioctl.c

@@ -3243,6 +3243,7 @@ static void btrfs_double_extent_lock(struct inode *inode1, u64 loff1,
 static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
 				   struct inode *dst, u64 dst_loff)
 {
+	const u64 bs = BTRFS_I(src)->root->fs_info->sb->s_blocksize;
 	int ret;
 
 	/*
@@ -3250,7 +3251,7 @@ static int btrfs_extent_same_range(struct inode *src, u64 loff, u64 len,
 	 * source range to serialize with relocation.
 	 */
 	btrfs_double_extent_lock(src, loff, dst, dst_loff, len);
-	ret = btrfs_clone(src, dst, loff, len, len, dst_loff, 1);
+	ret = btrfs_clone(src, dst, loff, len, ALIGN(len, bs), dst_loff, 1);
 	btrfs_double_extent_unlock(src, loff, dst, dst_loff, len);
 
 	return ret;

fs/read_write.c

@@ -1777,10 +1777,9 @@ static int remap_verify_area(struct file *file, loff_t pos, loff_t len,
  * else.  Assume that the offsets have already been checked for block
  * alignment.
  *
- * For deduplication we always scale down to the previous block because we
- * can't meaningfully compare post-EOF contents.
- *
- * For clone we only link a partial EOF block above the destination file's EOF.
+ * For clone we only link a partial EOF block above or at the destination file's
+ * EOF.  For deduplication we accept a partial EOF block only if it ends at the
+ * destination file's EOF (can not link it into the middle of a file).
  *
  * Shorten the request if possible.
  */
@@ -1796,8 +1795,7 @@ static int generic_remap_check_len(struct inode *inode_in,
 	if ((*len & blkmask) == 0)
 		return 0;
 
-	if ((remap_flags & REMAP_FILE_DEDUP) ||
-	    pos_out + *len < i_size_read(inode_out))
+	if (pos_out + *len < i_size_read(inode_out))
 		new_len &= ~blkmask;
 
 	if (new_len == *len)