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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 78F16C4338F for ; Fri, 30 Jul 2021 04:13:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5451661008 for ; Fri, 30 Jul 2021 04:13:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230043AbhG3ENv (ORCPT ); Fri, 30 Jul 2021 00:13:51 -0400 Received: from foss.arm.com ([217.140.110.172]:35928 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229465AbhG3ENu (ORCPT ); Fri, 30 Jul 2021 00:13:50 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5725931B; Thu, 29 Jul 2021 21:13:46 -0700 (PDT) Received: from [10.163.66.9] (unknown [10.163.66.9]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3CDD93F73D; Thu, 29 Jul 2021 21:13:42 -0700 (PDT) Subject: Re: [PATCH v2 03/10] coresight: etm-pmu: Ensure the AUX handle is valid To: Suzuki K Poulose , coresight@lists.linaro.org Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tamas.zsoldos@arm.com, al.grant@arm.com, leo.yan@linaro.org, mike.leach@linaro.org, mathieu.poirier@linaro.org, jinlmao@qti.qualcomm.com References: <20210723124611.3828908-1-suzuki.poulose@arm.com> <20210723124611.3828908-4-suzuki.poulose@arm.com> From: Anshuman Khandual Message-ID: Date: Fri, 30 Jul 2021 09:44:31 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210723124611.3828908-4-suzuki.poulose@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/23/21 6:16 PM, Suzuki K Poulose wrote: > The ETM perf infrastructure closes out a handle during event_stop > or on an error in starting the event. In either case, it is possible > for a "sink" to update/close the handle, under certain circumstances. > (e.g no space in ring buffer.). So, ensure that we handle this > gracefully in the PMU driver by verifying the handle is still valid. > > Cc: Mathieu Poirier > Cc: Mike Leach > Cc: Anshuman Khandual > Cc: Leo Yan > Signed-off-by: Suzuki K Poulose > --- > .../hwtracing/coresight/coresight-etm-perf.c | 27 ++++++++++++++++--- > 1 file changed, 24 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c > index 6f398377fec9..a6ab603afee4 100644 > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c > @@ -450,8 +450,15 @@ static void etm_event_start(struct perf_event *event, int flags) > fail_disable_path: > coresight_disable_path(path); > fail_end_stop: > - perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED); > - perf_aux_output_end(handle, 0); > + /* > + * Check if the handle is still associated with the event, > + * to handle cases where if the sink failed to start the > + * trace and TRUNCATED the handle already. > + */ > + if (READ_ONCE(handle->event)) { > + perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED); > + perf_aux_output_end(handle, 0); > + } Makes sense as perf_aux_output_[flag|end]() helpers do not validate the 'handle' themselves. > fail: > event->hw.state = PERF_HES_STOPPED; > goto out; > @@ -519,7 +526,21 @@ static void etm_event_stop(struct perf_event *event, int mode) > > size = sink_ops(sink)->update_buffer(sink, handle, > event_data->snk_config); > - perf_aux_output_end(handle, size); > + /* > + * Make sure the handle is still valid as the > + * sink could have closed it from an IRQ. > + * The sink driver must handle the race with > + * update_buffer() and IRQ. Thus either we > + * should get a valid handle and valid size > + * (which may be 0). > + * > + * But we should never get a non-zero size with > + * an invalid handle. > + */ > + if (READ_ONCE(handle->event)) > + perf_aux_output_end(handle, size); > + else > + WARN_ON(size); Right. > } > > /* Disabling the path make its elements available to other sessions */ > Reviewed-by: Anshuman Khandual