linux-kernel - [PATCH rcu 3/5] rcu-tasks: Mark ->trc_reader_special.b.need

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Date:   Wed, 21 Jul 2021 13:38:16 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 3/5] rcu-tasks: Mark ->trc_reader_special.b.need_qs data races

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.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tasks.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index f6b5320c44849..1cece5e9be9a9 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -850,7 +850,7 @@ static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
 /* 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)
@@ -916,7 +916,7 @@ static void trc_read_check_handler(void *t_in)
 	// 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:
@@ -968,7 +968,7 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
 	// 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;
 }
@@ -1103,7 +1103,7 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
 		 ".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);
 }
-- 
2.31.1.189.g2e36527f23