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. > > 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@xxxxxxxxxxx> > Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> > 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) > --- > kernel/time/timer.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 55 insertions(+), 5 deletions(-) > > --- a/kernel/time/timer.c > +++ b/kernel/time/timer.c > @@ -1202,6 +1230,9 @@ EXPORT_SYMBOL(timer_reduce); > * > * If @timer->expires is already in the past @timer will be queued to > * expire at the next timer tick. > + * > + * If @timer->function == NULL then the start operation is silently > + * discarded. > */ > void add_timer(struct timer_list *timer) > { Could you move the new paragraph after the paragraph where is is mentioned, that timer->function has to be set prior calling add_timer()? Thanks, Anna-Maria
