[PATCH RFC 07/16] rcu: Use this_cpu_{read,write}() for ->cpu_no_qs.b.exp

["Paul E. McKenney" <paulmck@kernel.org>]

Currently __this_cpu_read() and __this_cpu_write() is used to access the
->cpu_no_qs.b.exp field of the per-CPU rcu_data structure.  However,
this can fail when the accesses can happen in interrupt handlers, as
recently started being exercised by rcutorture.  This commit therefore
upgrades the uses of __this_cpu_read() and __this_cpu_write() to their
interrupt-safe counterparts this_cpu_read() and this_cpu_write().

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_exp.h    | 4 ++--
 kernel/rcu/tree_plugin.h | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 82cada459e5d0c..e03cb3d447a57d 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -731,7 +731,7 @@ static void rcu_exp_need_qs(void)
 {
 	lockdep_assert_irqs_disabled();
 	ASSERT_EXCLUSIVE_WRITER_SCOPED(*this_cpu_ptr(&rcu_data.cpu_no_qs.b.exp));
-	__this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
+	this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
 	/* Store .exp before .rcu_urgent_qs. */
 	smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
 	set_need_resched_current();
@@ -870,7 +870,7 @@ static void rcu_exp_handler(void *unused)
 
 	ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp);
 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
-	    __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+	    this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 		return;
 	if (rcu_is_cpu_rrupt_from_idle() ||
 	    (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9ba136a4233a26..c3db1ad4a2807a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -599,7 +599,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
  */
 static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
-	return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) ||
+	return (this_cpu_read(rcu_data.cpu_no_qs.b.exp) ||
 		READ_ONCE(t->rcu_read_unlock_special.s)) &&
 	       rcu_preempt_depth() == 0;
 }
@@ -981,7 +981,7 @@ static void rcu_qs(void)
 	trace_rcu_grace_period(TPS("rcu_sched"),
 			       __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
 	__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
-	if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+	if (this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 }
 
-- 
2.40.1