tjh.dev / kernel
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timers: Provide a better debugobjects hint for delayed works

With debugobjects enabled the timer hint for freeing of active timers
embedded inside delayed works is always the same, i.e. the hint is
delayed_work_timer_fn, even though the function the delayed work is going
to run can be wildly different depending on what work was queued. Enabling
workqueue debugobjects doesn't help either because the delayed work isn't
considered active until it is actually queued to run on a workqueue. If the
work is freed while the timer is pending the work isn't considered active
so there is no information from workqueue debugobjects.

Special case delayed works in the timer debugobjects hint logic so that the
delayed work function is returned instead of the delayed_work_timer_fn.
This will help to understand which delayed work was pending that got
freed.

Apply the same treatment for kthread_delayed_work because it follows the
same pattern.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220511201951.42408-1-swboyd@chromium.org

authored by

Stephen Boyd and committed by
Thomas Gleixner 317f29c1 f4b62e1e

+31 -1
+31 -1
kernel/time/timer.c
··· 638 638 639 639 static const struct debug_obj_descr timer_debug_descr; 640 640 641 + struct timer_hint { 642 + void (*function)(struct timer_list *t); 643 + long offset; 644 + }; 645 + 646 + #define TIMER_HINT(fn, container, timr, hintfn) \ 647 + { \ 648 + .function = fn, \ 649 + .offset = offsetof(container, hintfn) - \ 650 + offsetof(container, timr) \ 651 + } 652 + 653 + static const struct timer_hint timer_hints[] = { 654 + TIMER_HINT(delayed_work_timer_fn, 655 + struct delayed_work, timer, work.func), 656 + TIMER_HINT(kthread_delayed_work_timer_fn, 657 + struct kthread_delayed_work, timer, work.func), 658 + }; 659 + 641 660 static void *timer_debug_hint(void *addr) 642 661 { 643 - return ((struct timer_list *) addr)->function; 662 + struct timer_list *timer = addr; 663 + int i; 664 + 665 + for (i = 0; i < ARRAY_SIZE(timer_hints); i++) { 666 + if (timer_hints[i].function == timer->function) { 667 + void (**fn)(void) = addr + timer_hints[i].offset; 668 + 669 + return *fn; 670 + } 671 + } 672 + 673 + return timer->function; 644 674 } 645 675 646 676 static bool timer_is_static_object(void *addr)