Re: deleting timer that re-registers itself

From: "Valdis Klētnieks" <valdis.kletnieks@vt.edu>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: kernelnewbies@kernelnewbies.org
Subject: Re: deleting timer that re-registers itself
Date: Tue, 04 May 2021 12:17:56 -0400	[thread overview]
Message-ID: <323231.1620145076@turing-police> (raw)
In-Reply-To: <CAB=+i9QMD-PxCgR6sOBU+6ddtiMsqFQ5_bLTok=4q509cdE1sA@mail.gmail.com>

[-- Attachment #1.1: Type: text/plain, Size: 981 bytes --]

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);
}

[-- Attachment #1.2: Type: application/pgp-signature, Size: 832 bytes --]

[-- Attachment #2: Type: text/plain, Size: 170 bytes --]

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies