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

Anna-Maria Behnsen
2022-11-23T11:07:22Z

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.
>
> 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
> 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.
>
> Add debug_assert_init() instead of the WARN_ON_ONCE(!timer->function)
> checks so that debug objects can warn about non-initialized timers.

Could you expand this paragraph, so that is is not missleading when a
reader is not aware of the details of debug objects? Otherwise it seems to
the reader that debug objects will warn when timer->function == NULL.

The warning of debug objects does not cover the original
WARN_ON_ONCE(!timer->function). It warns when timer was not initialized
using timer_setup[_on_stack]() or via DEFINE_TIMER().

> 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.

Thanks,

Anna-Maria