smb3: fix cached file size problems in duplicate extents (reflink)

There were two problems (one of which could cause data corruption)
that were noticed with duplicate extents (ie reflink)
when debugging why various xfstests were being incorrectly skipped
(e.g. generic/138, generic/140, generic/142). First, we were not
updating the file size locally in the cache when extending a
file due to reflink (it would refresh after actimeo expires)
but xfstest was checking the size immediately which was still
0 so caused the test to be skipped.  Second, we were setting
the target file size (which could shrink the file) in all cases
to the end of the reflinked range rather than only setting the
target file size when reflink would extend the file.

CC: <stable@vger.kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -2038,6 +2038,7 @@ smb2_duplicate_extents(const unsigned int xid,
 {
 	int rc;
 	unsigned int ret_data_len;
+	struct inode *inode;
 	struct duplicate_extents_to_file dup_ext_buf;
 	struct cifs_tcon *tcon = tlink_tcon(trgtfile->tlink);
 
@@ -2054,10 +2055,21 @@ smb2_duplicate_extents(const unsigned int xid,
 	cifs_dbg(FYI, "Duplicate extents: src off %lld dst off %lld len %lld\n",
 		src_off, dest_off, len);
 
-	rc = smb2_set_file_size(xid, tcon, trgtfile, dest_off + len, false);
-	if (rc)
-		goto duplicate_extents_out;
+	inode = d_inode(trgtfile->dentry);
+	if (inode->i_size < dest_off + len) {
+		rc = smb2_set_file_size(xid, tcon, trgtfile, dest_off + len, false);
+		if (rc)
+			goto duplicate_extents_out;
 
+		/*
+		 * Although also could set plausible allocation size (i_blocks)
+		 * here in addition to setting the file size, in reflink
+		 * it is likely that the target file is sparse. Its allocation
+		 * size will be queried on next revalidate, but it is important
+		 * to make sure that file's cached size is updated immediately
+		 */
+		cifs_setsize(inode, dest_off + len);
+	}
 	rc = SMB2_ioctl(xid, tcon, trgtfile->fid.persistent_fid,
 			trgtfile->fid.volatile_fid,
 			FSCTL_DUPLICATE_EXTENTS_TO_FILE,