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: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 346321a..53946b1 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -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);

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c6ea81c..b5ba148 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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);

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 55f9b84..43dc688 100644 (file)
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -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. */