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 64C79C83F12 for ; Mon, 28 Aug 2023 13:55:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229906AbjH1Nyf (ORCPT ); Mon, 28 Aug 2023 09:54:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35624 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231135AbjH1NyZ (ORCPT ); Mon, 28 Aug 2023 09:54:25 -0400 Received: from mail-wr1-x435.google.com (mail-wr1-x435.google.com [IPv6:2a00:1450:4864:20::435]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88999D3; Mon, 28 Aug 2023 06:54:23 -0700 (PDT) Received: by mail-wr1-x435.google.com with SMTP id ffacd0b85a97d-31c5a2e8501so2753502f8f.0; Mon, 28 Aug 2023 06:54:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1693230862; x=1693835662; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:from:to:cc:subject:date:message-id:reply-to; bh=VDmYVoW7p8nt38CD6BvN3r9xzwRS5n00QRgr4Mi9/VU=; b=gh19/ymTWEypbg+l+oO/hboSV74tUyLQ0AC8+z/dSbPcrdsdoAEIFf1tJGhznWzcC4 22hoUj9kwlKuIPRkPWFiWqDC43IwjqblEsJsw7kuScda0OX/mb3/SWWdBP8x8XEBbSul U7/iUmCNv/1u29JCo4OrYvzVo/8AeGkcW7nkQTdKKx/dW2PNh6Dt8uOlRfdtiMFTXSnz EyYEcLfWXsFNLfoYuyT/Ol0dwn6HUURaQykY7kKzQAXQOu8PqbnBIK973YdW8M5Kqbs9 ST3lt338LPkp927J5DZb2+nV08aGccoX9hay9v7r5MfefAn/+8ml1hEVVhqwdIGQE+sX UXsw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693230862; x=1693835662; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=VDmYVoW7p8nt38CD6BvN3r9xzwRS5n00QRgr4Mi9/VU=; b=S6vyDs6KpND5gnOz2FEopIsEWA1oEc1d0fRRYI3W3x1cqX58iQxvmK+OmmmMKyT9h2 +kAMBxg/nxf4ikYnJ1P7yJmYoMt2bWAtMUrTj4JZN8aXmQeL1TSAO6QGgTaG0/XV5dE7 KGTsVDzPn1rDNT7ePeUWp4gQ/qYFka+OFaaPVeT33QsfvCLKahQ75bcASDrx57FGE8+I Qdr4FMWEp+UNePoX2PTbg0mBPQStEA2KgDVS6hYt/fjjjL+d3sbC1jF5vTuTB5TQxt6n Marbib0EjoG4+T/tNOYPbkJshLqy7qYk27S3uLxpEHjqpSkBVucH1BFRi9gx7pswtD02 cwcg== X-Gm-Message-State: AOJu0Yz+WepC8xY4UGOFAUUJ0w5/eLCgGXspGhQXHo6ep3BTrIYj3oxM 3PcAoF5MPEEImfiTmdnXyms= X-Google-Smtp-Source: AGHT+IG95nW6xPk0zV6WB4OItUlDjsx3dUBybv6nT1PqBfrGNAkcz36bK6VacMecutGOK5zkit30bA== X-Received: by 2002:adf:ce8e:0:b0:313:ef24:6fe6 with SMTP id r14-20020adfce8e000000b00313ef246fe6mr20110183wrn.1.1693230861671; Mon, 28 Aug 2023 06:54:21 -0700 (PDT) Received: from krava ([83.240.61.245]) by smtp.gmail.com with ESMTPSA id bf8-20020a0564021a4800b00529fb5fd3b9sm4478223edb.80.2023.08.28.06.54.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Aug 2023 06:54:21 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 28 Aug 2023 15:54:18 +0200 To: Rong Tao Cc: olsajiri@gmail.com, alexandre.torgue@foss.st.com, andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, chantr4@gmail.com, daniel@iogearbox.net, deso@posteo.net, eddyz87@gmail.com, haoluo@google.com, iii@linux.ibm.com, john.fastabend@gmail.com, kpsingh@kernel.org, laoar.shao@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, martin.lau@linux.dev, mcoquelin.stm32@gmail.com, mykolal@fb.com, rongtao@cestc.cn, sdf@google.com, shuah@kernel.org, song@kernel.org, xukuohai@huawei.com, yonghong.song@linux.dev, zwisler@google.com Subject: Re: [PATCH bpf-next v8] selftests/bpf: trace_helpers.c: optimize kallsyms cache Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 28, 2023 at 08:57:21AM +0800, Rong Tao wrote: > Hi, jirka. Thanks for your reply. > > > > @@ -164,13 +165,14 @@ int main(int argc, char **argv) > > > } > > > > > > /* initialize kernel symbol translation */ > > > - if (load_kallsyms()) { > > > + ksyms = load_kallsyms(); > > > > if we keep the load_kallsyms/ksym_search/ksym_get_addr functions as described > > in [1] the samples/bpf would stay untouched apart from the Makefile change > > Maybe we should make this modification, wouldn't it be better? After all, > not modifying the source code of samples/bpf is not really a reason not to > make modifications to load_kallsyms(), what do you think? I think we want separate selftest and samples changes and I don't see other way to do that > > In addition, if we continue to keep the original ksym_search() interface, > the following problems are very difficult to deal with: > > Source code ksym_search [1] > > struct ksym *ksym_search(long key) > { > int start = 0, end = sym_cnt; > int result; > > /* kallsyms not loaded. return NULL */ > if (sym_cnt <= 0) > return NULL; > > while (start < end) { > size_t mid = start + (end - start) / 2; > > result = key - syms[mid].addr; > if (result < 0) > end = mid; > else if (result > 0) > start = mid + 1; > else > return &syms[mid]; <<< > } > > if (start >= 1 && syms[start - 1].addr < key && > key < syms[start].addr) > /* valid ksym */ > return &syms[start - 1]; <<< > > /* out of range. return _stext */ > return &syms[0]; <<< > } > > The original ksym_search() interface directly returns the global syms > address, which is also dangerous for multi-threading. If we allocate new > memory for this, it is not a perfect solution. the assumption was that the original ksym_search touches the global syms allocated before running tests.. then tests that actually need fresh kallsyms data (because of bpf_testmod load/unload) would get their own copy of kallsyms jirka > > If we rewrite > > struct ksym *ksym_search(long key) > > to > struct ksym ksym_search(long key) > > This also affects the source code in samples/bpf. > > The same problem exists with ksym_get_addr(). > > Best wishes, > Rong Tao > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/trace_helpers.c#n100 > >