staging/lustre/xattr: xattr data may be gone with lock held

Xattr cached data may be gone, but lock still held, in this case,
refetch xattr from server, otherwise client will return error.
Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-on: http://review.whamcloud.com/12952
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3544Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/xattr_cache.c

@@ -295,13 +295,18 @@ static int ll_xattr_find_get_lock(struct inode *inode,
 
 
 	mutex_lock(&lli->lli_xattrs_enq_lock);
-	/* Try matching first. */
-	mode = ll_take_md_lock(inode, MDS_INODELOCK_XATTR, &lockh, 0, LCK_PR);
-	if (mode != 0) {
-		/* fake oit in mdc_revalidate_lock() manner */
-		oit->d.lustre.it_lock_handle = lockh.cookie;
-		oit->d.lustre.it_lock_mode = mode;
-		goto out;
+	/* inode may have been shrunk and recreated, so data is gone, match lock
+	 * only when data exists. */
+	if (ll_xattr_cache_valid(lli)) {
+		/* Try matching first. */
+		mode = ll_take_md_lock(inode, MDS_INODELOCK_XATTR, &lockh, 0,
+				       LCK_PR);
+		if (mode != 0) {
+			/* fake oit in mdc_revalidate_lock() manner */
+			oit->d.lustre.it_lock_handle = lockh.cookie;
+			oit->d.lustre.it_lock_mode = mode;
+			goto out;
+		}
 	}
 
 	/* Enqueue if the lock isn't cached locally. */