From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752804Ab3C0OJs (ORCPT ); Wed, 27 Mar 2013 10:09:48 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:41121 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751310Ab3C0OJr (ORCPT ); Wed, 27 Mar 2013 10:09:47 -0400 Message-ID: <1364393372.5053.68.camel@laptop> Subject: Re: BUG: using smp_processor_id() in preemptible [00000000] code: asm/8267 From: Peter Zijlstra To: Borislav Petkov Cc: Namhyung Kim , Ingo Molnar , Arnaldo Carvalho de Melo , lkml , Stephane Eranian , Namhyung Kim , Jiri Olsa Date: Wed, 27 Mar 2013 15:09:32 +0100 In-Reply-To: <20130327094932.GA8385@pd.tnic> References: <20130324115556.GA4866@pd.tnic> <20130324155924.GB4866@pd.tnic> <20130326183452.GC27518@pd.tnic> <87ip4dgz31.fsf@sejong.aot.lge.com> <20130327094932.GA8385@pd.tnic> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(); }