[CIFS] Don't cache timestamps on utimes due to coarse granularity

force revalidate of the file when any of the timestamps are set since
some filesytem types do not have finer granularity timestamps and
we can not always detect which file systems round timestamps down
to determine whether we can cache the mtime on setattr
samba bugzilla 3775
Acked-by: NShirish Pargaonkar <sharishp@us.ibm.com>
Signed-off-by: NSteve French <sfrench@us.ibm.com>

fs/cifs/inode.c

@@ -1762,8 +1762,18 @@ cifs_setattr_unix(struct dentry *direntry, struct iattr *attrs)
 					CIFS_MOUNT_MAP_SPECIAL_CHR);
 	}
 
-	if (!rc)
+	if (!rc) {
 		rc = inode_setattr(inode, attrs);
+
+		/* force revalidate when any of these times are set since some
+		   of the fs types (eg ext3, fat) do not have fine enough
+		   time granularity to match protocol, and we do not have a
+		   a way (yet) to query the server fs's time granularity (and
+		   whether it rounds times down).
+		*/
+		if (!rc && (attrs->ia_valid & (ATTR_MTIME | ATTR_CTIME)))
+			cifsInode->time = 0;
+	}
 out:
 	kfree(args);
 	kfree(full_path);