gfs2: Fix remote demote of weak glock holders

When we mock up a temporary holder in gfs2_glock_cb to demote weak holders in
response to a remote locking conflict, we don't set the HIF_HOLDER flag.  This
causes function may_grant to BUG.  Fix by setting the missing HIF_HOLDER flag
in the mock glock holder.

In addition, define the mock glock holder where it is used.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -1857,7 +1857,6 @@ void gfs2_glock_dq_m(unsigned int num_gh, struct gfs2_holder *ghs)
 
 void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
 {
-	struct gfs2_holder mock_gh = { .gh_gl = gl, .gh_state = state, };
 	unsigned long delay = 0;
 	unsigned long holdtime;
 	unsigned long now = jiffies;
@@ -1890,8 +1889,13 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
 	 * keep the glock until the last strong holder is done with it.
 	 */
 	if (!find_first_strong_holder(gl)) {
-		if (state == LM_ST_UNLOCKED)
-			mock_gh.gh_state = LM_ST_EXCLUSIVE;
+		struct gfs2_holder mock_gh = {
+			.gh_gl = gl,
+			.gh_state = (state == LM_ST_UNLOCKED) ?
+				    LM_ST_EXCLUSIVE : state,
+			.gh_iflags = BIT(HIF_HOLDER)
+		};
+
 		demote_incompat_holders(gl, &mock_gh);
 	}
 	handle_callback(gl, state, delay, true);