Re: [patch V2 12/17] timers: Silently ignore timers with a NULL function

Anna-Maria Behnsen
2022-11-23T09:23:32Z

On Tue, 22 Nov 2022, Thomas Gleixner wrote:

> Tearing down timers which have circular dependencies to other
> functionality, e.g. workqueues, where the timer can schedule work and work
> can arm timers is not trivial.

NIT (comma is missing): can arm timer, is not trivial.

> In those cases it is desired to shutdown the timer in a way which prevents
> rearming of the timer. The mechanism to do so it to set timer->function to

s/to do so it/to do so is/

> NULL and use this as an indicator for the timer arming functions to ignore
> the (re)arm request.
>
> In preparation for that replace the warnings in the relevant code pathes
> with checks for timer->function == NULL and discard the rearm request
> silently.

Here is a verb missing that this is a grammatically correct (and
understandable) sentence.

> Add debug_assert_init() instead of the WARN_ON_ONCE(!timer->function)
> checks so that debug objects can warn about non-initialized timers.
>
> If developers fail to enable debug objects and then waste lots of time to
> figure out why their non-initialized timer is not firing, they deserve it.
>
> Co-developed-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home
> Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org
> ---
> V2: Use continue instead of return and amend the return value docs (Steven)
> ---
> kernel/time/timer.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 55 insertions(+), 5 deletions(-)
>
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1128,8 +1144,12 @@ static inline int
> * mod_timer_pending() is the same for pending timers as mod_timer(), but
> * will not activate inactive timers.
> *
> + * If @timer->function == NULL then the start operation is silently
> + * discarded.
> + *
> * Return:
> - * * %0 - The timer was inactive and not modified
> + * * %0 - The timer was inactive and not modified or was is in
> + * shutdown state and the operation was discarded

Do you mean "was" or "is"? Please have also a look at the places where you
use the same phrase.

> * * %1 - The timer was active and requeued to expire at @expires
> */
> int mod_timer_pending(struct timer_list *timer, unsigned long expires)
> @@ -1155,8 +1175,12 @@ EXPORT_SYMBOL(mod_timer_pending);
> * same timer, then mod_timer() is the only safe way to modify the timeout,
> * since add_timer() cannot modify an already running timer.
> *
> + * If @timer->function == NULL then the start operation is silently
> + * discarded, the return value is 0 and meaningless.

It's easier to read, if you make a dot instead of comma.

Thanks,

Anna-Maria