[PATCH 5.10 330/509] rcu-tasks: Mark ->trc_reader_special.b.need_qs data races

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From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

[ Upstream commit f8ab3fad80dddf3f2cecb53983063c4431058ca1 ]

There are several ->trc_reader_special.b.need_qs data races that are
too low-probability for KCSAN to notice, but which will happen sooner
or later.  This commit therefore marks these accesses.

Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/rcu/tasks.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -801,7 +801,7 @@ static DEFINE_IRQ_WORK(rcu_tasks_trace_i
 /* If we are the last reader, wake up the grace-period kthread. */
 void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
 {
-	int nq = t->trc_reader_special.b.need_qs;
+	int nq = READ_ONCE(t->trc_reader_special.b.need_qs);
 
 	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) &&
 	    t->trc_reader_special.b.need_mb)
@@ -867,7 +867,7 @@ static void trc_read_check_handler(void
 	// Get here if the task is in a read-side critical section.  Set
 	// its state so that it will awaken the grace-period kthread upon
 	// exit from that critical section.
-	WARN_ON_ONCE(t->trc_reader_special.b.need_qs);
+	WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs));
 	WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
 
 reset_ipi:
@@ -919,7 +919,7 @@ static bool trc_inspect_reader(struct ta
 	// state so that it will awaken the grace-period kthread upon exit
 	// from that critical section.
 	atomic_inc(&trc_n_readers_need_end); // One more to wait on.
-	WARN_ON_ONCE(t->trc_reader_special.b.need_qs);
+	WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs));
 	WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
 	return true;
 }
@@ -1048,7 +1048,7 @@ static void show_stalled_task_trace(stru
 		 ".i"[is_idle_task(t)],
 		 ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)],
 		 READ_ONCE(t->trc_reader_nesting),
-		 " N"[!!t->trc_reader_special.b.need_qs],
+		 " N"[!!READ_ONCE(t->trc_reader_special.b.need_qs)],
 		 cpu);
 	sched_show_task(t);
 }





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