Commit 8ff37290 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add *_ONCE() for grace-period progress indicators 



The various RCU structures' ->gp_seq, ->gp_seq_needed, ->gp_req_activity,
and ->gp_activity fields are read locklessly, so they must be updated with
WRITE_ONCE() and, when read locklessly, with READ_ONCE().  This commit makes
these changes.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent bfeebe24

kernel/rcu/tree.c

+7 −7
Original line number Diff line number Diff line
@@ -1175,7 +1175,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, 
					  TPS("Prestarted"));

			goto unlock_out;

		}

		rnp->gp_seq_needed = gp_seq_req;

		WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);

		if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {

			/*

			 * We just marked the leaf or internal node, and a
@@ -1210,8 +1210,8 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, 
unlock_out:

	/* Push furthest requested GP to leaf node and rcu_data structure. */

	if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {

		rnp_start->gp_seq_needed = rnp->gp_seq_needed;

		rdp->gp_seq_needed = rnp->gp_seq_needed;

		WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);

		WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);

	}

	if (rnp != rnp_start)

		raw_spin_unlock_rcu_node(rnp);
@@ -1423,7 +1423,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) 
	}

	rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */

	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)

		rdp->gp_seq_needed = rnp->gp_seq_needed;

		WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);

	WRITE_ONCE(rdp->gpwrap, false);

	rcu_gpnum_ovf(rnp, rdp);

	return ret;
@@ -3276,12 +3276,12 @@ int rcutree_prepare_cpu(unsigned int cpu) 
	rnp = rdp->mynode;

	raw_spin_lock_rcu_node(rnp);		/* irqs already disabled. */

	rdp->beenonline = true;	 /* We have now been online. */

	rdp->gp_seq = rnp->gp_seq;

	rdp->gp_seq_needed = rnp->gp_seq;

	rdp->gp_seq = READ_ONCE(rnp->gp_seq);

	rdp->gp_seq_needed = rdp->gp_seq;

	rdp->cpu_no_qs.b.norm = true;

	rdp->core_needs_qs = false;

	rdp->rcu_iw_pending = false;

	rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;

	rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;

	trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));

	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	rcu_prepare_kthreads(cpu);

kernel/rcu/tree_plugin.h

+1 −1
Original line number Diff line number Diff line
@@ -753,7 +753,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) 
	raw_lockdep_assert_held_rcu_node(rnp);

	pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",

		__func__, rnp->grplo, rnp->grphi, rnp->level,

		(long)rnp->gp_seq, (long)rnp->completedqs);

		(long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);

	for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)

		pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",

			__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);

kernel/rcu/tree_stall.h

+15 −11
Original line number Diff line number Diff line
@@ -592,21 +592,22 @@ void show_rcu_gp_kthreads(void) 
		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),

		READ_ONCE(rcu_state.gp_flags));

	rcu_for_each_node_breadth_first(rnp) {

		if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))

		if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),

				 READ_ONCE(rnp->gp_seq_needed)))

			continue;

		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",

			rnp->grplo, rnp->grphi, (long)rnp->gp_seq,

			(long)rnp->gp_seq_needed);

			rnp->grplo, rnp->grphi, (long)READ_ONCE(rnp->gp_seq),

			(long)READ_ONCE(rnp->gp_seq_needed));

		if (!rcu_is_leaf_node(rnp))

			continue;

		for_each_leaf_node_possible_cpu(rnp, cpu) {

			rdp = per_cpu_ptr(&rcu_data, cpu);

			if (rdp->gpwrap ||

			    ULONG_CMP_GE(rcu_state.gp_seq,

					 rdp->gp_seq_needed))

			    ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),

					 READ_ONCE(rdp->gp_seq_needed)))

				continue;

			pr_info("\tcpu %d ->gp_seq_needed %ld\n",

				cpu, (long)rdp->gp_seq_needed);

				cpu, (long)READ_ONCE(rdp->gp_seq_needed));

		}

	}

	for_each_possible_cpu(cpu) {
@@ -631,7 +632,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, 
	static atomic_t warned = ATOMIC_INIT(0);



	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||

	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))

	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),

			 READ_ONCE(rnp_root->gp_seq_needed)))

		return;

	j = jiffies; /* Expensive access, and in common case don't get here. */

	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
@@ -642,7 +644,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, 
	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	j = jiffies;

	if (rcu_gp_in_progress() ||

	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||

	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),

			 READ_ONCE(rnp_root->gp_seq_needed)) ||

	    time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||

	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||

	    atomic_read(&warned)) {
@@ -655,9 +658,10 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, 
		raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */

	j = jiffies;

	if (rcu_gp_in_progress() ||

	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||

	    time_before(j, rcu_state.gp_req_activity + gpssdelay) ||

	    time_before(j, rcu_state.gp_activity + gpssdelay) ||

	    ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),

			 READ_ONCE(rnp_root->gp_seq_needed)) ||

	    time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||

	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||

	    atomic_xchg(&warned, 1)) {

		if (rnp_root != rnp)

			/* irqs remain disabled. */

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