Re: deleting timer that re-registers itself

May 4, 2021

      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

Re: deleting timer that re-registers itself

Greg KH