Re: [patch V3 12/17] timers: Silently ignore timers with a NULL function
From: Anna-Maria Behnsen <anna-maria@linutronix.de>
Date: 2022-11-24 07:37:44
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linux-bluetooth, lkml
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
quoted hunk ↗ jump to hunk
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@goodmis.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Thomas Gleixner <redacted> Tested-by: Guenter Roeck <linux@roeck-us.net> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home (local) Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org (local) --- 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