gfs2: Fix deadlock dumping resource group glocks

Commit 0e539ca ("gfs2: Fix NULL pointer dereference in gfs2_rgrp_dump")
introduced additional locking in gfs2_rgrp_go_dump, which is also used for
dumping resource group glocks via debugfs.  However, on that code path, the
glock spin lock is already taken in dump_glock, and taking it again in
gfs2_glock2rgrp leads to deadlock.  This can be reproduced with:

  $ mkfs.gfs2 -O -p lock_nolock /dev/FOO
  $ mount /dev/FOO /mnt/foo
  $ touch /mnt/foo/bar
  $ cat /sys/kernel/debug/gfs2/FOO/glocks

Fix that by not taking the glock spin lock inside the go_dump callback.

Fixes: 0e539ca ("gfs2: Fix NULL pointer dereference in gfs2_rgrp_dump")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

Author: Alexander Aring

fs/gfs2/glops.c

@@ -245,7 +245,7 @@ static void rgrp_go_inval(struct gfs2_glock *gl, int flags)
 static void gfs2_rgrp_go_dump(struct seq_file *seq, struct gfs2_glock *gl,
 			      const char *fs_id_buf)
 {
-	struct gfs2_rgrpd *rgd = gfs2_glock2rgrp(gl);
+	struct gfs2_rgrpd *rgd = gl->gl_object;
 
 	if (rgd)
 		gfs2_rgrp_dump(seq, rgd, fs_id_buf);