Btrfs: btrfs_ioctl_clone: Truncate complete page after performing clone operation

In subpagesize-blocksize scenario, the "destination offset" argument passed to
the btrfs_ioctl_clone() can be aligned to sectorsize but may not be
necessarily aligned to the machine's page size. In such cases,
truncate_inode_pages_range() ends up zeroing out the partial page and future
read operations will return incorrect data. Hence this commit explicitly
rounds down the "destination offset" to the machine's page size.
Signed-off-by: NChandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -3926,8 +3926,9 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	 * Truncate page cache pages so that future reads will see the cloned
 	 * data immediately and not the previous data.
 	 */
-	truncate_inode_pages_range(&inode->i_data, destoff,
-				   PAGE_CACHE_ALIGN(destoff + len) - 1);
+	truncate_inode_pages_range(&inode->i_data,
+				round_down(destoff, PAGE_CACHE_SIZE),
+				round_up(destoff + len, PAGE_CACHE_SIZE) - 1);
 out_unlock:
 	if (!same_inode)
 		btrfs_double_inode_unlock(src, inode);