gfs2: Allow gfs2_xattr_set to be called with the glock held

On the following call path:

  gfs2_setattr -> setattr_prepare -> ... ->
    cap_inode_killpriv -> ... ->
      gfs2_xattr_set

the glock is locked in gfs2_setattr, so check for recursive locking in
gfs2_xattr_set as gfs2_xattr_get already does.  While at it, get rid of
need_unlock in gfs2_xattr_get.

Fixes xfstest generic/093.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Abhijith Das <adas@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/xattr.c

@@ -610,7 +610,6 @@ static int gfs2_xattr_get(const struct xattr_handler *handler,
 {
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_holder gh;
-	bool need_unlock = false;
 	int ret;
 
 	/* During lookup, SELinux calls this function with the glock locked. */
@@ -619,10 +618,11 @@ static int gfs2_xattr_get(const struct xattr_handler *handler,
 		ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &gh);
 		if (ret)
 			return ret;
-		need_unlock = true;
+	} else {
+		gfs2_holder_mark_uninitialized(&gh);
 	}
 	ret = __gfs2_xattr_get(inode, name, buffer, size, handler->flags);
-	if (need_unlock)
+	if (gfs2_holder_initialized(&gh))
 		gfs2_glock_dq_uninit(&gh);
 	return ret;
 }
@@ -1244,10 +1244,19 @@ static int gfs2_xattr_set(const struct xattr_handler *handler,
 	if (ret)
 		return ret;
 
+	/* May be called from gfs_setattr with the glock locked. */
+
+	if (!gfs2_glock_is_locked_by_me(ip->i_gl)) {
 		ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &gh);
 		if (ret)
 			return ret;
+	} else {
+		if (WARN_ON_ONCE(ip->i_gl->gl_state != LM_ST_EXCLUSIVE))
+			return -EIO;
+		gfs2_holder_mark_uninitialized(&gh);
+	}
 	ret = __gfs2_xattr_set(inode, name, value, size, flags, handler->flags);
+	if (gfs2_holder_initialized(&gh))
 		gfs2_glock_dq_uninit(&gh);
 	return ret;
 }