gfs2: Don't call dlm after protocol is unmounted

In the gfs2 withdraw sequence, the dlm protocol is unmounted with a call
to lm_unmount. After a withdraw, users are allowed to unmount the
withdrawn file system. But at that point we may still have glocks left
over that we need to free via unmount's call to gfs2_gl_hash_clear.
These glocks may have never been completed because of whatever problem
caused the withdraw (IO errors or whatever).

Before this patch, function gdlm_put_lock would still try to call into
dlm to unlock these leftover glocks, which resulted in dlm returning
-EINVAL because the lock space was abandoned. These glocks were never
freed because there was no mechanism after that to free them.

This patch adds a check to gdlm_put_lock to see if the locking protocol
was inactive (DFL_UNMOUNT flag) and if so, free the glock and not
make the invalid call into dlm.

I could have combined this "if" with the one that follows, related to
leftover glock LVBs, but I felt the code was more readable with its own
if clause.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/lock_dlm.c

@@ -299,6 +299,11 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 	gfs2_sbstats_inc(gl, GFS2_LKS_DCOUNT);
 	gfs2_update_request_times(gl);
 
+	/* don't want to call dlm if we've unmounted the lock protocol */
+	if (test_bit(DFL_UNMOUNT, &ls->ls_recover_flags)) {
+		gfs2_glock_free(gl);
+		return;
+	}
 	/* don't want to skip dlm_unlock writing the lvb when lock has one */
 
 	if (test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags) &&