Messages in this thread Patch in this message | | | Subject | Re: BUG: using smp_processor_id() in preemptible [00000000] code: asm/8267 | From | Peter Zijlstra <> | Date | Wed, 27 Mar 2013 15:09:32 +0100 |
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On Wed, 2013-03-27 at 10:49 +0100, Borislav Petkov wrote: > Ok, just for my own understanding: how do the events on the > ->task_ctx->event_list relate to the current cpu in this path? I mean, > we're on the task exit path here so is it possible to be rescheduled > somewhere else and the check in event_filter_match to become > meaningless?
Events can be per-cpu, so what could happen is that we'd send the exit notification to a cpu we're not actually running on (anymore).
Furthermore, since we evaluate smp_processor_id() for every event_filter_match(), it is possible we'd send the notification to multiple events if our task migrates just right.
Also, I suspect we want something like preempt_disable_notrace() to be sure we don't recurse or something daft like that... but I'm not entirely sure.
--- kernel/events/core.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 7b4a55d..0097d81 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4444,19 +4444,22 @@ static void perf_event_task_event(struct perf_task_event *task_event) perf_event_task_ctx(&cpuctx->ctx, task_event); ctx = task_event->task_ctx; - if (!ctx) { - ctxn = pmu->task_ctx_nr; - if (ctxn < 0) - goto next; - ctx = rcu_dereference(current->perf_event_ctxp[ctxn]); - if (ctx) - perf_event_task_ctx(ctx, task_event); - } + if (ctx) + goto next; + ctxn = pmu->task_ctx_nr; + if (ctxn < 0) + goto next; + ctx = rcu_dereference(current->perf_event_ctxp[ctxn]); + if (ctx) + perf_event_task_ctx(ctx, task_event); next: put_cpu_ptr(pmu->pmu_cpu_context); } - if (task_event->task_ctx) + if (task_event->task_ctx) { + preempt_disable_notrace(); perf_event_task_ctx(task_event->task_ctx, task_event); + preempt_enable_notrace(); + } rcu_read_unlock(); }
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