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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: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-05-24 12:48:18 -07:00
parent 45f4b4a202
commit bdb0cca0d1
1 changed files with 6 additions and 5 deletions
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11
kernel/rcu/tasks.h
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@ -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);