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=-3.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_NEOMUTT 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 DB8C4C282C3 for ; Fri, 25 Jan 2019 02:57:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAF4B218D9 for ; Fri, 25 Jan 2019 02:57:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="NO8UbBP1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728907AbfAYC5F (ORCPT ); Thu, 24 Jan 2019 21:57:05 -0500 Received: from mail-pf1-f194.google.com ([209.85.210.194]:43354 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725991AbfAYC5F (ORCPT ); Thu, 24 Jan 2019 21:57:05 -0500 Received: by mail-pf1-f194.google.com with SMTP id w73so4006245pfk.10 for ; Thu, 24 Jan 2019 18:57:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=1ZTfeh56EvXSJOEsIVRYuKkDoVKsIXZKXpowOcMtxAk=; b=NO8UbBP1w+MxZVPmlIraGu6+NTflnpXTpNaLaX1mVf4R+41oU0xHBhNUo1M3LgwSWC 3y4KoS54nj94fDr1JiMW6oLZBfrHV0qkTLcJLAABliilSSiUZJYIJ63000YogZaajXhA pxw5M9lGRd7+wLuPh2OswAvRqU/2/hYOOqeUlJZyXIOoXhKVpCfC/WR9/Qn+Fp/Ok9ba DuA9YdIxKafMH+njxDdus9lsgPff/+FgoIRJseaEiHiVsqlrvFm+TH3gkef0WfhIZupe Gwb6AZFAB9cTTF3J5301Ei7zGBJEtr56y4ho2/8xYMHCKP2iRTxtVB+a/dzPLB8J5IKd +aNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=1ZTfeh56EvXSJOEsIVRYuKkDoVKsIXZKXpowOcMtxAk=; b=A2Y44QgEsbcTG9NQmadRdKE2Q0rUUoV56Ta4oWhWF+JNalkrdWExD54EqcJcCkcc4F VKyAQ1iYqdWqo0BkoByXDDQIOArJDE4d4HAH7GMzE5p2Ba0+StKLqqt9A9zHzF4zSBrW ZBkfCC8x+c7ZkT6FnCwMu+eE9/SPF3fdltDrTkFcNSTFA4yh3G+OSW8oeIKSIgxQm32Y Edm+Cv9/kx3lDjI3jyrsXEdh5Tfeo0DY0S7gqJF3FnHGEDhSAlNIsh8QJ6EBZlpk63nF 8ZZkjP7hz+jLfVD0UhAtLP2OccuF5nQdWJTSnpyaG8uBqRk+oXCbpd5FW2lZDcqigmgs Oicw== X-Gm-Message-State: AJcUukddeId26nivtPagmCqEG0uEghtnjwDWs3578iObAPwtFiNg6OB6 wKaJoCLvyPvcnnDBPPRZyLc= X-Google-Smtp-Source: ALg8bN4Tzj91tBCvhTb8vU3hp5jbxg39Syyslv1khXJ+a3nt9fMQyEHr4CmKCEFcHMxMT0hzvR2aoA== X-Received: by 2002:a62:1212:: with SMTP id a18mr9412491pfj.217.1548385022456; Thu, 24 Jan 2019 18:57:02 -0800 (PST) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:200::7:5429]) by smtp.gmail.com with ESMTPSA id 6sm47846809pfv.30.2019.01.24.18.57.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Jan 2019 18:57:01 -0800 (PST) Date: Thu, 24 Jan 2019 18:57:00 -0800 From: Alexei Starovoitov To: Eric Dumazet Cc: Peter Zijlstra , Alexei Starovoitov , davem@davemloft.net, daniel@iogearbox.net, jakub.kicinski@netronome.com, netdev@vger.kernel.org, kernel-team@fb.com, mingo@redhat.com, will.deacon@arm.com, Paul McKenney , jannh@google.com Subject: Re: [PATCH v4 bpf-next 1/9] bpf: introduce bpf_spin_lock Message-ID: <20190125025659.netyncl6vvtbv6oj@ast-mbp.dhcp.thefacebook.com> References: <20190124041403.2100609-1-ast@kernel.org> <20190124041403.2100609-2-ast@kernel.org> <20190124180109.GA27771@hirez.programming.kicks-ass.net> <20190124235857.xyb5xx2ufr6x5mbt@ast-mbp.dhcp.thefacebook.com> <395a3741-70c9-c345-08a4-77bc3bd3cae2@gmail.com> <20190125023402.34a5k62furpdismi@ast-mbp.dhcp.thefacebook.com> <9e1fa851-e189-ab17-ae34-236cc6b5a8b4@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9e1fa851-e189-ab17-ae34-236cc6b5a8b4@gmail.com> User-Agent: NeoMutt/20180223 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Jan 24, 2019 at 06:44:20PM -0800, Eric Dumazet wrote: > > > On 01/24/2019 06:34 PM, Alexei Starovoitov wrote: > > On Thu, Jan 24, 2019 at 06:29:55PM -0800, Eric Dumazet wrote: > >> > >> > >> On 01/24/2019 03:58 PM, Alexei Starovoitov wrote: > >>> On Thu, Jan 24, 2019 at 07:01:09PM +0100, Peter Zijlstra wrote: > >> > >>>> and from NMI ... > >>> > >>> progs are not preemptable and map syscall accessors have bpf_prog_active counters. > >>> So nmi/kprobe progs will not be running when syscall is running. > >>> Hence dead lock is not possible and irq_save is not needed. > >> > >> > >> Speaking of NMI, how pcpu_freelist_push() and pop() can actually work ? > >> > >> It seems bpf_get_stackid() can be called from NMI, and lockdep seems to complain loudly > > > > it's a known false positive. > > https://lkml.org/lkml/2018/7/25/756 > > and the same answer as before: > > we're not going to penalize performance to shut up false positive. > > > > As far as lockdep is concerned, I do not believe we care about performance. > > How can we remove this false positive, so that lockdep stays alive even after running bpf test_progs ? Like do irq_save version when lockdep is on? Sure. Let's do that. That splat was bugging me for very long time. I see it every single day when I run this test before applying patches. > Let see if we understood this well. > > 1. create perf event PERF_TYPE_HARDWARE:PERF_COUNT_HW_CPU_CYCLES > 2. attach bpf probram to this event > 3. since that's a hw event, the bpf program is executed in NMI context > 4. the bpf program calls bpf_get_stackid to record the trace in a bpf map > 5. bpf_get_stackid calls pcpu_freelist_pop and pcpu_freelist_push from NMI > 6. userspace calls sys_bpf(bpf_map_lookup_elem) which calls bpf_stackmap_copy which can call pcpu_freelist_push argh. lookup cmd is missing __this_cpu_inc(bpf_prog_active); like update/delete do. Will fix. > It seems pcpu_freelist_pop and pcpu_freelist_push are not NMI safe, > so what prevents bad things to happen ? nmi checks for bpf_prog_active==0. See bpf_overflow_handler.