On Tue, May 04, 2021 at 12:17:56PM -0400, Valdis Klētnieks wrote:
> On Tue, 04 May 2021 23:59:12 +0900, Hyeonggon Yoo said:
> > Does del_timer work well for timers that re-registers itself?
> > what if the timer is currently running, and del_timer is called,
> > and the running timer re-registers itself?
>
> Minor nit: while the timer is running, there's no problem.
> When the timer has *expired* and timer_callback() is running
> is when you have a race condition.
>
> So who's going to call del_timer()? The only thing that does that is
> timer_exit. Soo... Apply some silly locking:
>
> static int exiting = 0;
>
> void timer_callback(struct timer_list *timer) {
> struct timer_data *data = from_timer(data, timer, timer);
> data->value++;
> printk(KERN_INFO "[%s] value is = %d\n", __func__, data->value);
> if (!exiting)
> mod_timer(timer, jiffies + DELAY);
> }
>
> void __exit timer_exit(void) {
> exiting = 1;
> int ret = del_timer(&data.timer);
> printk("[%s] deleting timer..., ret = %d\n", __func__, ret);
> }
That's mean, don't write buggy code as an example because then I'm going
to have to reject it when it gets submitted as a "real" driver :)
Hint, a "global" variable like this does not work like you expect it to
at all, sorry.
greg k-h
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