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 AACE7C677F1 for ; Mon, 9 Jan 2023 04:02:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234208AbjAIECU (ORCPT ); Sun, 8 Jan 2023 23:02:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54004 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236253AbjAIECT (ORCPT ); Sun, 8 Jan 2023 23:02:19 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6FD42CE1C; Sun, 8 Jan 2023 20:02:17 -0800 (PST) Received: from dggpemm500006.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Nr0bv1fszzJrLy; Mon, 9 Jan 2023 12:00:59 +0800 (CST) Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.34; Mon, 9 Jan 2023 12:02:14 +0800 Subject: Re: [PATCH 2/3] bpf: Optimize get_modules_for_addrs() To: Petr Mladek , Song Liu CC: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Joe Lawrence , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Steven Rostedt , Masami Hiramatsu , Mark Rutland , , , , , Luis Chamberlain , References: <20221230112729.351-1-thunder.leizhen@huawei.com> <20221230112729.351-3-thunder.leizhen@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <4447b3b1-8023-3100-da6b-1f399e50005f@huawei.com> Date: Mon, 9 Jan 2023 12:02:13 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2023/1/5 17:05, Petr Mladek wrote: > On Wed 2023-01-04 09:07:02, Song Liu wrote: >> On Wed, Jan 4, 2023 at 8:25 AM Petr Mladek wrote: >>> >>> On Fri 2022-12-30 19:27:28, Zhen Lei wrote: >>>> Function __module_address() can quickly return the pointer of the module >>>> to which an address belongs. We do not need to traverse the symbols of all >>>> modules to check whether each address in addrs[] is the start address of >>>> the corresponding symbol, because register_fprobe_ips() will do this check >>>> later. >>>> >>>> Assuming that there are m modules, each module has n symbols on average, >>>> and the number of addresses 'addrs_cnt' is abbreviated as K. Then the time >>>> complexity of the original method is O(K * log(K)) + O(m * n * log(K)), >>>> and the time complexity of current method is O(K * (log(m) + M)), M <= m. >>>> (m * n * log(K)) / (K * m) ==> n / log2(K). Even if n is 10 and K is 128, >>>> the ratio is still greater than 1. Therefore, the new method will >>>> generally have better performance. >>>> >>>> Signed-off-by: Zhen Lei >>>> --- >>>> kernel/trace/bpf_trace.c | 101 ++++++++++++++++----------------------- >>>> 1 file changed, 40 insertions(+), 61 deletions(-) >>>> >>>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >>>> index 5f3be4bc16403a5..0ff9037098bd241 100644 >>>> --- a/kernel/trace/bpf_trace.c >>>> +++ b/kernel/trace/bpf_trace.c >>>> @@ -2684,69 +2684,55 @@ static void symbols_swap_r(void *a, void *b, int size, const void *priv) >>>> } >>>> } >>>> >>>> -struct module_addr_args { >>>> - unsigned long *addrs; >>>> - u32 addrs_cnt; >>>> - struct module **mods; >>>> - int mods_cnt; >>>> - int mods_cap; >>>> -}; >>>> - >>>> -static int module_callback(void *data, const char *name, >>>> - struct module *mod, unsigned long addr) >>>> +static int get_modules_for_addrs(struct module ***out_mods, unsigned long *addrs, u32 addrs_cnt) >>>> { >>>> - struct module_addr_args *args = data; >>>> - struct module **mods; >>>> - >>>> - /* We iterate all modules symbols and for each we: >>>> - * - search for it in provided addresses array >>>> - * - if found we check if we already have the module pointer stored >>>> - * (we iterate modules sequentially, so we can check just the last >>>> - * module pointer) >>>> - * - take module reference and store it >>>> - */ >>>> - if (!bsearch(&addr, args->addrs, args->addrs_cnt, sizeof(addr), >>>> - bpf_kprobe_multi_addrs_cmp)) >>>> - return 0; >>>> + int i, j, err; >>>> + int mods_cnt = 0; >>>> + int mods_cap = 0; >>>> + struct module *mod; >>>> + struct module **mods = NULL; >>>> >>>> - if (args->mods && args->mods[args->mods_cnt - 1] == mod) >>>> - return 0; >>>> + for (i = 0; i < addrs_cnt; i++) { >>>> + mod = __module_address(addrs[i]); >>> >>> This must be called under module_mutex to make sure that the module >>> would not disappear. >> >> module_mutex is not available outside kernel/module/. The common >> practice is to disable preempt before calling __module_address(). >> CONFIG_LOCKDEP should catch this. > > I see. Sigh, it is always better to take mutex than disable > preemption. But it might be acceptable in this case. We just need > to be careful. > > First, the preemption must stay disabled all the time until > try_module_get(). Otherwise the returned struct module could > disappear in the meantime. > > Second, krealloc_array() has to be called with preemption > enabled. It is perfectly fine to do it after try_module_get(). Okay, thanks for the heads-up. > > Best Regards, > Petr > . > -- Regards, Zhen Lei