gfs2: Fix unlikely race in gdlm_put_lock

In gdlm_put_lock(), there is a small window of time in which the
DFL_UNMOUNT flag has been set but the lockspace hasn't been released,
yet.  In that window, dlm may still call gdlm_ast() and gdlm_bast().
To prevent it from dereferencing freed glock objects, only free the
glock if the lockspace has actually been released.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Andrew Price <anprice@redhat.com>

Author: Andreas Gruenbacher

fs/gfs2/lock_dlm.c

@@ -344,12 +344,6 @@ 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;
-	}
-
 	/*
 	 * When the lockspace is released, all remaining glocks will be
 	 * unlocked automatically.  This is more efficient than unlocking them
@@ -379,6 +373,11 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 		goto again;
 	}
 
+	if (error == -ENODEV) {
+		gfs2_glock_free(gl);
+		return;
+	}
+
 	if (error) {
 		fs_err(sdp, "gdlm_unlock %x,%llx err=%d\n",
 		       gl->gl_name.ln_type,