Re: [PATCH 4.19 089/114] hrtimer: Annotate lockless access to timer->state

Hi!

From: Eric Dumazet edumazet@google.com

commit 56144737e67329c9aaed15f942d46a6302e2e3d8 upstream.

syzbot reported various data-race caused by hrtimer_is_queued() reading timer->state. A READ_ONCE() is required there to silence the warning.

Also add the corresponding WRITE_ONCE() when timer->state is set.

In remove_hrtimer() the hrtimer_is_queued() helper is open coded to avoid loading timer->state twice.

Is there a reason why READ_ONCE is not neccessary in remove_hrtimer?

Should there be comment there explaining it?

Best regards, Pavel

@@ -1002,8 +1004,9 @@ static void __remove_hrtimer(struct hrti static inline int remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base, bool restart) {

• if (hrtimer_is_queued(timer)) {

• u8 state = timer->state;
  

• u8 state = timer->state;
• if (state & HRTIMER_STATE_ENQUEUED) { int reprogram;

/*