Commit bdb0cca0 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Mark ->trc_reader_nesting data races 



There are several ->trc_reader_nesting data races that are too
low-probability for KCSAN to notice, but which will happen sooner or
later.  This commit therefore marks these accesses, and comments one
that cannot race.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 45f4b4a2

kernel/rcu/tasks.h

+6 −5
Original line number Diff line number Diff line
@@ -897,7 +897,7 @@ static void trc_read_check_handler(void *t_in) 


	// If the task is not in a read-side critical section, and

	// if this is the last reader, awaken the grace-period kthread.

	if (likely(!t->trc_reader_nesting)) {

	if (likely(!READ_ONCE(t->trc_reader_nesting))) {

		if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))

			wake_up(&trc_wait);

		// Mark as checked after decrement to avoid false
@@ -906,7 +906,7 @@ static void trc_read_check_handler(void *t_in) 
		goto reset_ipi;

	}

	// If we are racing with an rcu_read_unlock_trace(), try again later.

	if (unlikely(t->trc_reader_nesting < 0)) {

	if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0)) {

		if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))

			wake_up(&trc_wait);

		goto reset_ipi;
@@ -953,6 +953,7 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg) 
			n_heavy_reader_ofl_updates++;

		in_qs = true;

	} else {

		// The task is not running, so C-language access is safe.

		in_qs = likely(!t->trc_reader_nesting);

	}
@@ -985,7 +986,7 @@ static void trc_wait_for_one_reader(struct task_struct *t, 
	// The current task had better be in a quiescent state.

	if (t == current) {

		t->trc_reader_checked = true;

		WARN_ON_ONCE(t->trc_reader_nesting);

		WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));

		return;

	}
@@ -1101,7 +1102,7 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) 
		 ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0],

		 ".i"[is_idle_task(t)],

		 ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)],

		 t->trc_reader_nesting,

		 READ_ONCE(t->trc_reader_nesting),

		 " N"[!!t->trc_reader_special.b.need_qs],

		 cpu);

	sched_show_task(t);
@@ -1196,7 +1197,7 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) 
static void exit_tasks_rcu_finish_trace(struct task_struct *t)

{

	WRITE_ONCE(t->trc_reader_checked, true);

	WARN_ON_ONCE(t->trc_reader_nesting);

	WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));

	WRITE_ONCE(t->trc_reader_nesting, 0);

	if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))

		rcu_read_unlock_trace_special(t, 0);