On Wed, 23 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 is 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 paths > with checks for timer->function == NULL. If the pointer is NULLL, then s/NULLL/NULL > 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. > > The warning of debug objects does warn if timer->function == NULL. It does NOT warn > 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. Same for initializing a timer with a NULL function. > > Co-developed-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> > Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx> > Link: https://lore.kernel.org/all/20220407161745.7d6754b3@xxxxxxxxxxxxxxxxxx > Link: https://lore.kernel.org/all/20221110064101.429013735@xxxxxxxxxxx > --- > V2: Use continue instead of return and amend the return value docs (Steven) > V3: Changelog and comment updates (Anna-Maria) > --- > kernel/time/timer.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 52 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 You forgot to update this "was is" mistake. All other places are fine. > * * %1 - The timer was active and requeued to expire at @expires > */ > int mod_timer_pending(struct timer_list *timer, unsigned long expires) Thanks, Anna-Maria
