[PATCH] cpu/hotplug: mark concurrent accesses to should_run

[Zhu Jun]

The boot processor sets should_run to wake the application processor's
hotplug thread. cpuhp_should_run() reads that flag without a common lock.
The existing memory barriers order the associated state, but do not mark
the flag accesses themselves, which KCSAN reports as a data race.

Use READ_ONCE() and WRITE_ONCE() for should_run accesses while preserving
the existing barriers and completion protocol.

Fixes: 4cb28ced23c4 ("cpu/hotplug: Create hotplug threads")
Signed-off-by: Zhu Jun <zhujun2@xxxxxxxxxxxxxxxxxxxx>
---
 kernel/cpu.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 376d297a6292..ab8dae116e0e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -774,7 +774,7 @@ static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
 	 * true. Paired with the mb() above in cpuhp_thread_fun()
 	 */
 	smp_mb();
-	st->should_run = true;
+	WRITE_ONCE(st->should_run, true);
 	wake_up_process(st->thread);
 	wait_for_ap_thread(st, st->bringup);
 }
@@ -1045,7 +1045,7 @@ static int cpuhp_should_run(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
 
-	return st->should_run;
+	return READ_ONCE(st->should_run);
 }
 
 /*
@@ -1068,7 +1068,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 	bool bringup = st->bringup;
 	enum cpuhp_state state;
 
-	if (WARN_ON_ONCE(!st->should_run))
+	if (WARN_ON_ONCE(!READ_ONCE(st->should_run)))
 		return;
 
 	/*
@@ -1087,10 +1087,11 @@ static void cpuhp_thread_fun(unsigned int cpu)
 
 	if (st->single) {
 		state = st->cb_state;
-		st->should_run = false;
+		WRITE_ONCE(st->should_run, false);
 	} else {
-		st->should_run = cpuhp_next_state(bringup, &state, st, st->target);
-		if (!st->should_run)
+		WRITE_ONCE(st->should_run,
+			   cpuhp_next_state(bringup, &state, st, st->target));
+		if (!READ_ONCE(st->should_run))
 			goto end;
 	}
 
@@ -1116,14 +1117,14 @@ static void cpuhp_thread_fun(unsigned int cpu)
 		 * playing.
 		 */
 		WARN_ON_ONCE(st->rollback);
-		st->should_run = false;
+		WRITE_ONCE(st->should_run, false);
 	}
 
 end:
 	cpuhp_lock_release(bringup);
 	lockdep_release_cpus_lock();
 
-	if (!st->should_run)
+	if (!READ_ONCE(st->should_run))
 		complete_ap_thread(st, bringup);
 }
 
-- 
2.51.0