Commit 2431774f authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Mark accesses to rcu_state.n_force_qs 



This commit marks accesses to the rcu_state.n_force_qs.  These data
races are hard to make happen, but syzkaller was equal to the task.

Reported-by: default avatar <syzbot+e08a83a1940ec3846cd5@syzkaller.appspotmail.com>
Acked-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 6880fa6c

kernel/rcu/tree.c

+5 −5
Original line number Diff line number Diff line
@@ -1907,7 +1907,7 @@ static void rcu_gp_fqs(bool first_time) 
	struct rcu_node *rnp = rcu_get_root();



	WRITE_ONCE(rcu_state.gp_activity, jiffies);

	rcu_state.n_force_qs++;

	WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);

	if (first_time) {

		/* Collect dyntick-idle snapshots. */

		force_qs_rnp(dyntick_save_progress_counter);
@@ -2550,7 +2550,7 @@ static void rcu_do_batch(struct rcu_data *rdp) 
	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */

	if (count == 0 && rdp->qlen_last_fqs_check != 0) {

		rdp->qlen_last_fqs_check = 0;

		rdp->n_force_qs_snap = rcu_state.n_force_qs;

		rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);

	} else if (count < rdp->qlen_last_fqs_check - qhimark)

		rdp->qlen_last_fqs_check = count;
@@ -2898,10 +2898,10 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, 
		} else {

			/* Give the grace period a kick. */

			rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;

			if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&

			if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&

			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)

				rcu_force_quiescent_state();

			rdp->n_force_qs_snap = rcu_state.n_force_qs;

			rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);

			rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);

		}

	}
@@ -4128,7 +4128,7 @@ int rcutree_prepare_cpu(unsigned int cpu) 
	/* Set up local state, ensuring consistent view of global state. */

	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	rdp->qlen_last_fqs_check = 0;

	rdp->n_force_qs_snap = rcu_state.n_force_qs;

	rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);

	rdp->blimit = blimit;

	rdp->dynticks_nesting = 1;	/* CPU not up, no tearing. */

	rcu_dynticks_eqs_online();