[PATCH RFC 12/16] rcu: Mark interrupts-enabled accesses to rdp->cpu_no_qs.b.norm

The rdp->cpu_no_qs.b.norm field is accessed only by the current CPU,
but can be accessed both at task level and from interrupt handlers.
All accesses from interrupts-enabled code must therefore be marked.
This commit therefore converts from __this_cpu_read() to this_cpu_read(),
from __this_cpu_write() to this_cpu_write(), and plain C-language accesses
to READ_ONCE() and WRITE_ONCE(), but only in interrupts-enabled code.

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <[email protected]>
---
 kernel/rcu/tree.c        | 2 +-
 kernel/rcu/tree_plugin.h | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c9780e7c0e2afa..377153e0d93440 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2540,7 +2540,7 @@ rcu_check_quiescent_state(struct rcu_data *rdp)
 	 * Was there a quiescent state since the beginning of the grace
 	 * period? If no, then exit and wait for the next call.
 	 */
-	if (rdp->cpu_no_qs.b.norm)
+	if (READ_ONCE(rdp->cpu_no_qs.b.norm))
 		return;
 
 	/*
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c3db1ad4a2807a..353effac5a37f1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -298,11 +298,11 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 static void rcu_qs(void)
 {
 	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
-	if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {
+	if (this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {
 		trace_rcu_grace_period(TPS("rcu_preempt"),
 				       __this_cpu_read(rcu_data.gp_seq),
 				       TPS("cpuqs"));
-		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
+		this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
 		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
 		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
 	}
@@ -952,7 +952,7 @@ void rcu_read_unlock_strict(void)
 	 * __rcu_read_unlock().
 	 */
 	rdp = this_cpu_ptr(&rcu_data);
-	rdp->cpu_no_qs.b.norm = false;
+	WRITE_ONCE(rdp->cpu_no_qs.b.norm, false);
 	rcu_report_qs_rdp(rdp);
 	udelay(rcu_unlock_delay);
 }
@@ -980,7 +980,7 @@ static void rcu_qs(void)
 		return;
 	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);
+	this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
 	if (this_cpu_read(rcu_data.cpu_no_qs.b.exp))
 		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
 }
-- 
2.40.1