From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B674BC07520 for ; Thu, 13 Sep 2018 07:53:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 74FE520881 for ; Thu, 13 Sep 2018 07:53:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 74FE520881 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727600AbeIMNCA (ORCPT ); Thu, 13 Sep 2018 09:02:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55004 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726842AbeIMNB7 (ORCPT ); Thu, 13 Sep 2018 09:01:59 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3D9DD90C9F; Thu, 13 Sep 2018 07:53:42 +0000 (UTC) Received: from krava (unknown [10.43.17.10]) by smtp.corp.redhat.com (Postfix) with SMTP id 77E971001F40; Thu, 13 Sep 2018 07:53:40 +0000 (UTC) Date: Thu, 13 Sep 2018 09:53:39 +0200 From: Jiri Olsa To: Peter Zijlstra Cc: Jiri Olsa , Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Namhyung Kim , Alexander Shishkin , Andi Kleen Subject: Re: [PATCH] perf: Prevent recursion in ring buffer Message-ID: <20180913075339.GC15173@krava> References: <20180912193317.10339-1-jolsa@kernel.org> <20180913074042.GU24124@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180913074042.GU24124@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 13 Sep 2018 07:53:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 13, 2018 at 09:40:42AM +0200, Peter Zijlstra wrote: > On Wed, Sep 12, 2018 at 09:33:17PM +0200, Jiri Olsa wrote: > > > # perf record -e 'sched:sched_switch,sched:sched_wakeup' perf bench sched messaging > > > The reason for the corruptions are some of the scheduling tracepoints, > > that have __perf_task dfined and thus allow to store data to another > > cpu ring buffer: > > > > sched_waking > > sched_wakeup > > sched_wakeup_new > > sched_stat_wait > > sched_stat_sleep > > sched_stat_iowait > > sched_stat_blocked > > > And then iterates events of the 'task' and store the sample > > for any task's event that passes tracepoint checks: > > > > ctx = rcu_dereference(task->perf_event_ctxp[perf_sw_context]); > > > > list_for_each_entry_rcu(event, &ctx->event_list, event_entry) { > > if (event->attr.type != PERF_TYPE_TRACEPOINT) > > continue; > > if (event->attr.config != entry->type) > > continue; > > > > perf_swevent_event(event, count, &data, regs); > > } > > > > Above code can race with same code running on another cpu, > > ending up with 2 cpus trying to store under the same ring > > buffer, which is not handled at the moment. > > It can yes, however the only way I can see this breaking is if we use > !inherited events with a strict per-task buffer, but your record command > doesn't use that. > > Now, your test-case uses inherited events, which would all share the > buffer, however IIRC inherited events require per-task-per-cpu buffers, that's what perf record always does when monitoring task.. there's an event/rb for each cpu and the given task and all events for the task (sched:*) on given cpu share that single cpu ring buffer via PERF_EVENT_IOC_SET_OUTPUT > because there is already no guarantee the various tasks run on the same > CPU in the first place. > > This means we _should_ write to the @task's local CPU buffer, and that > would work again. > > Let me try and figure out where this is going wrong.