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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C8729EB64DB for ; Thu, 15 Jun 2023 06:58:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243947AbjFOG6G (ORCPT ); Thu, 15 Jun 2023 02:58:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238189AbjFOG6C (ORCPT ); Thu, 15 Jun 2023 02:58:02 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 75C68DF; Wed, 14 Jun 2023 23:58:00 -0700 (PDT) Received: from kwepemm600003.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QhY2l2msNztQxw; Thu, 15 Jun 2023 14:55:27 +0800 (CST) Received: from [10.67.111.205] (10.67.111.205) by kwepemm600003.china.huawei.com (7.193.23.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Thu, 15 Jun 2023 14:57:57 +0800 Subject: Re: [PATCH] perf top & record: Fix segfault when default cycles event is not supported To: Ian Rogers CC: , , , , , , , , , , References: <20230614151625.2077-1-yangjihong1@huawei.com> <668a6159-b7a8-ed25-d8fa-5584a4c04d37@huawei.com> From: Yang Jihong Message-ID: <325b3a4c-b17e-67a8-da31-d5033878a157@huawei.com> Date: Thu, 15 Jun 2023 14:57:56 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.205] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600003.china.huawei.com (7.193.23.202) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On 2023/6/15 10:04, Ian Rogers wrote: > On Wed, Jun 14, 2023 at 6:55 PM Yang Jihong wrote: >> >> Hello, >> >> On 2023/6/15 6:03, Ian Rogers wrote: >>> On Wed, Jun 14, 2023 at 9:18 AM Ian Rogers wrote: >>>> >>>> On Wed, Jun 14, 2023 at 8:18 AM Yang Jihong wrote: >>>>> >>>>> The perf-record and perf-top call parse_event() to add a cycles event to >>>>> an empty evlist. For the system that does not support hardware cycles >>>>> event, such as QEMU, the evlist is empty due to the following code process: >>>>> >>>>> parse_event(evlist, "cycles:P" or ""cycles:Pu") >>>>> parse_events(evlist, "cycles:P") >>>>> __parse_events >>>>> ... >>>>> ret = parse_events__scanner(str, &parse_state); >>>>> // ret = 0 >>>>> ... >>>>> ret2 = parse_events__sort_events_and_fix_groups() >>>>> if (ret2 < 0) >>>>> return ret; >>>>> // The cycles event is not supported, here ret2 = -EINVAL, >>>>> // Here return 0. >>>>> ... >>>>> evlist__splice_list_tail(evlist) >>>>> // The code here does not execute to, so the evlist is still empty. >>>>> >>>>> A null pointer occurs when the content in the evlist is accessed later. >>>>> >>>>> Before: >>>>> >>>>> # perf list hw >>>>> >>>>> List of pre-defined events (to be used in -e or -M): >>>>> >>>>> # perf record true >>>>> libperf: Miscounted nr_mmaps 0 vs 1 >>>>> WARNING: No sample_id_all support, falling back to unordered processing >>>>> perf: Segmentation fault >>>>> Obtained 1 stack frames. >>>>> [0xc5beff] >>>>> Segmentation fault >>>>> >>>>> Solution: >>>>> If cycles event is not supported, try to fall back to cpu-clock event. >>>>> >>>>> After: >>>>> # perf record true >>>>> [ perf record: Woken up 1 times to write data ] >>>>> [ perf record: Captured and wrote 0.006 MB perf.data ] >>>>> # >>>>> >>>>> Fixes: 7b100989b4f6 ("perf evlist: Remove __evlist__add_default") >>>>> Signed-off-by: Yang Jihong >>>> >>>> Thanks, useful addition. The cpu-clock fall back wasn't present before >>>> 7b100989b4f6 so is the fixes tag correct? >>> >>> Hmm... it should be coming from evsel__fallback: >>> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/evsel.c?h=tmp.perf-tools-next#n2840 >>> so we shouldn't duplicate that logic. The question is why we're not >>> doing the fallback. >>> >> >> Yes, it's a bit of the same logic as evsel__fallback, or we can call >> evlist__add_default() as before, simply create an evsel of hardware >> cycles and add it directly to evlist. >> >> Please confirm whether this solution is feasible. If it is feasible, I >> will send a v2 version. > > The previous evlist__add_default logic didn't handle wildcard PMUs for > cycles, hence wanting to reuse the parse events logic. The error is > that the logic now isn't doing the fallback properly. I think an > evlist__add_cycles which uses evsel__fallback makes sense matching the > previous logic. I'd be happy if you took a look. I'll write a patch so > that the perf_pmus list of core PMUs is never empty. Do you mean to do fallback when parsing events? Instead of doing it at evsel__open? Okay, I'll re-patch it with this solution, and it looks like it should work. Thanks, Yang