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=-0.6 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 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 3C99AECDE43 for ; Fri, 19 Oct 2018 14:47:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC40220869 for ; Fri, 19 Oct 2018 14:47:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ajaFMpao" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC40220869 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727592AbeJSWx6 (ORCPT ); Fri, 19 Oct 2018 18:53:58 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:36013 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726664AbeJSWx6 (ORCPT ); Fri, 19 Oct 2018 18:53:58 -0400 Received: by mail-wr1-f65.google.com with SMTP id y16so37744902wrw.3 for ; Fri, 19 Oct 2018 07:47:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=S+kqQcne43yBtKD0A4xPWMBbdtznaufs+fBWnD76mFs=; b=ajaFMpaoYsmG0R762tYUnDS3ksRvUUxalZbggHmdQC2PI9u6nq8evZSodJ/XAin/Wh XqbjxeKHlW2iHvn+sI2gzmNoelDy4u3qX7ZSleOKVwZkcHWoe1fADaJ+rKfkJA1MgfXi Jzzwesil0arauW0D1ynGEzK/EKqmxMkXYRHmXpHhsihBS2NjM+HBOBCL8Yyroy4bq6zV hpqreRvdzpRC829K4sw9n3Q22bYOEwDnCo37zs9vjG+7F/97pf34sdEiOARFp2vr5ofA CpDGk5OY5yq9zel17C4DDVe0KijNkCT3pF7EfhMBQKhscaHtOrnkWgrR4tuOTA3l0uJg v53g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=S+kqQcne43yBtKD0A4xPWMBbdtznaufs+fBWnD76mFs=; b=BpKemf3blsSiV+rDy/FgAMpGp3qgp2s2f15xPIO6XcNUmfyIEyDx5BlqayjxIjmFWX xq8OJfofuboFGkFz1N4IgDdn+7Tb506UZaOcIiJ/3PrmyodkMJCbuWt2AkC9bFkRqln2 SKKBRnMxka41rm8Uo7WWOPh/cBwqTaZi2Gpzb+2Ubt1TPw8eCjdx0TfXA1XhYzTS+Rn0 ZjBlOdFImjFfWEqg5y3gxZiVxfHfbK295lEwT0+fhjfbHIxrBn9tEUDCjn0OisCcRQlM r4wGoaXQZ9te2UopG+CcD1ubBzEYwNTYVkzOav9queKeARh+ftrMaUcQ+Fx1qcXT7MbB pRbw== X-Gm-Message-State: ABuFfojGmTUPjlACsvIiaDe4d0QaWOsLH+Y8MtFQbcs+Jn8vRl77fq5v OVmkdUF3dWynAHg8J3vgAsZrYaoTkIRERTpWWqg= X-Google-Smtp-Source: ACcGV634pvV/ZWhB3UDnctkJjOFMmd9ukQLKaEzSLetJJIKIg3mkncIqeEzdntN3xC8i9P2UjxqRVSMTZCKzlQRqT3U= X-Received: by 2002:adf:f712:: with SMTP id r18-v6mr34293605wrp.85.1539960450696; Fri, 19 Oct 2018 07:47:30 -0700 (PDT) MIME-Version: 1.0 References: <20181018005420.82993-1-namit@vmware.com> <20181018005420.82993-2-namit@vmware.com> <07255D2B-0243-4254-B62A-37050C44207E@vmware.com> <925F22EA-F8CB-4194-B96B-378409ED7918@vmware.com> <2626124E-7344-42F3-AD07-0BB34D62A9EE@amacapital.net> <6F1FD9DA-5E86-42A2-8EAF-05F5D70FE2EF@vmware.com> <20181019050051.bs2kk4sagu7hpwxx@ast-mbp.dhcp.thefacebook.com> <20181019082202.GB3121@hirez.programming.kicks-ass.net> In-Reply-To: <20181019082202.GB3121@hirez.programming.kicks-ass.net> From: Alexei Starovoitov Date: Fri, 19 Oct 2018 07:47:18 -0700 Message-ID: Subject: Re: [RFC PATCH 1/5] x86: introduce preemption disable prefix To: Peter Zijlstra Cc: Andy Lutomirski , Nadav Amit , Oleg Nesterov , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , LKML , X86 ML , Borislav Petkov , David Woodhouse , Daniel Borkmann , Roman Gushchin Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 19, 2018 at 1:22 AM Peter Zijlstra wrote: > > On Thu, Oct 18, 2018 at 10:00:53PM -0700, Alexei Starovoitov wrote: > > > > > > > > > > > Another example is __BPF_PROG_RUN_ARRAY(), which also uses > > > > preempt_enable_no_resched(). > > > > > > Alexei, I think this code is just wrong. > > > > why 'just wrong' ? > > Because you lost a preemption point, this is a no-no. > > > > > > Do you know why it uses > > > preempt_enable_no_resched()? > > > > dont recall precisely. > > we could be preemptable at the point where macro is called. > > I think the goal of no_resched was to avoid adding scheduling points > > where they didn't exist before just because a prog ran for few nsec. > > May be Daniel or Roman remember. > > No, you did the exact opposite, where there previously was a preemption, > you just ate it. The band saw didn't get stopped in time, you loose your > hand etc.. Let me do few experiments then. We will fix it up.