Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v2] locking/lock_events: Use this_cpu_add() when necessary | Date | Fri, 24 May 2019 12:53:46 -0400 |
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The kernel test robot has reported that the use of __this_cpu_add() causes bug messages like:
BUG: using __this_cpu_add() in preemptible [00000000] code: ...
This is only an issue on preempt kernel where preemption can happen in the middle of a percpu operation. We are still using __this_cpu_*() for !preempt kernel to avoid additional overhead in case CONFIG_PREEMPT_COUNT is set.
v2: Simplify the condition to just preempt or !preempt.
Fixes: a8654596f0371 ("locking/rwsem: Enable lock event counting") Signed-off-by: Waiman Long <longman@redhat.com> --- kernel/locking/lock_events.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h index feb1acc54611..05f34068ec06 100644 --- a/kernel/locking/lock_events.h +++ b/kernel/locking/lock_events.h @@ -30,13 +30,32 @@ enum lock_events { */ DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]); +/* + * The purpose of the lock event counting subsystem is to provide a low + * overhead way to record the number of specific locking events by using + * percpu counters. It is the percpu sum that matters, not specifically + * how many of them happens in each cpu. + * + * In !preempt kernel, we can just use __this_cpu_*() as preemption + * won't happen in the middle of the percpu operation. In preempt kernel, + * preemption happens in the middle of the percpu operation may produce + * incorrect result. + */ +#ifdef CONFIG_PREEMPT +#define lockevent_percpu_inc(x) this_cpu_inc(x) +#define lockevent_percpu_add(x, v) this_cpu_add(x, v) +#else +#define lockevent_percpu_inc(x) __this_cpu_inc(x) +#define lockevent_percpu_add(x, v) __this_cpu_add(x, v) +#endif + /* * Increment the PV qspinlock statistical counters */ static inline void __lockevent_inc(enum lock_events event, bool cond) { if (cond) - __this_cpu_inc(lockevents[event]); + lockevent_percpu_inc(lockevents[event]); } #define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true) @@ -44,7 +63,7 @@ static inline void __lockevent_inc(enum lock_events event, bool cond) static inline void __lockevent_add(enum lock_events event, int inc) { - __this_cpu_add(lockevents[event], inc); + lockevent_percpu_add(lockevents[event], inc); } #define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c) -- 2.18.1
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