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@kernel.org>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 2d3dc340b25af0e64f7d306b893e8485ca057acb..efb8127f3a36d20d586c017a5544a7d69a6948ad 100644 (file)
--- 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:
@@ -969,7 +969,7 @@ 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;
 }
@@ -1105,7 +1105,7 @@ 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);
 }