[tip: core/rcu] rcu: Add *_ONCE() for grace-period progress indicators

From: tip-bot2 for Paul E. McKenney
Date: Tue Mar 24 2020 - 05:17:56 EST

Next message: tip-bot2 for Paul E. McKenney: "[tip: core/rcu] rcu: Provide debug symbols and line numbers in KCSAN runs"
Previous message: tip-bot2 for Paul E. McKenney: "[tip: core/rcu] locktorture: Print ratio of acquisitions, not failures"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID: 8ff37290d6622e130553a38ec2662a728e46cdba
Gitweb: https://git.kernel.org/tip/8ff37290d6622e130553a38ec2662a728e46cdba
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Sat, 04 Jan 2020 11:33:17 -08:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Thu, 20 Feb 2020 15:58:22 -08:00

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@xxxxxxxxxx>
---
kernel/rcu/tree.c | 14 +++++++-------
kernel/rcu/tree_plugin.h | 2 +-
kernel/rcu/tree_stall.h | 26 +++++++++++++++-----------
3 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 346321a..53946b1 100644
--- 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
--- 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
--- 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. */

Next message: tip-bot2 for Paul E. McKenney: "[tip: core/rcu] rcu: Provide debug symbols and line numbers in KCSAN runs"
Previous message: tip-bot2 for Paul E. McKenney: "[tip: core/rcu] locktorture: Print ratio of acquisitions, not failures"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]