[PATCH 2/2] timers/migration: Mark updates to tmigr_event ->field

[Paul E. McKenney]

The tmigr_event structure's ->ignore field are sometimes accessed
locklessly, but the __tmigr_cpu_activate(), tmigr_cpu_new_timer(),
and __tmigr_cpu_deactivate() functions do not mark accesses to this field.

Therefore, use READ_ONCE() for the tmigr_cpu_new_timer() function's
lockless load and WRITE_ONCE() for the __tmigr_cpu_activate() and
__tmigr_cpu_deactivate() functions' stores.

KCSAN located this issue.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
---
 kernel/time/timer_migration.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
index 059d43355e65..f920e73fff51 100644
--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -715,7 +715,7 @@ static void __tmigr_cpu_activate(struct tmigr_cpu *tmc)
 
 	trace_tmigr_cpu_active(tmc);
 
-	tmc->cpuevt.ignore = true;
+	WRITE_ONCE(tmc->cpuevt.ignore, true);
 	WRITE_ONCE(tmc->wakeup, KTIME_MAX);
 
 	walk_groups(&tmigr_active_up, &data, tmc);
@@ -1258,7 +1258,7 @@ u64 tmigr_cpu_new_timer(u64 nextexp)
 	ret = READ_ONCE(tmc->wakeup);
 	if (nextexp != KTIME_MAX) {
 		if (nextexp != tmc->cpuevt.nextevt.expires ||
-		    tmc->cpuevt.ignore) {
+		    READ_ONCE(tmc->cpuevt.ignore)) {
 			ret = tmigr_new_timer(tmc, nextexp);
 			/*
 			 * Make sure the reevaluation of timers in idle path
@@ -1362,7 +1362,7 @@ static u64 __tmigr_cpu_deactivate(struct tmigr_cpu *tmc, u64 nextexp)
 	 * or CPU goes offline.
 	 */
 	if (nextexp != KTIME_MAX)
-		tmc->cpuevt.ignore = false;
+		WRITE_ONCE(tmc->cpuevt.ignore, false);
 
 	walk_groups(&tmigr_inactive_up, &data, tmc);
 	return data.firstexp;
-- 
2.40.1