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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 CDA7AC43331 for ; Fri, 27 Mar 2020 03:24:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 95CFA20714 for ; Fri, 27 Mar 2020 03:24:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585279462; bh=EJrO+ay23oFPaDm5e7voyfzo2zotMJYKFA+r8ofPtU8=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=TSViV3ZH1Mqnwkj3XguiyxP8nWxTeYip564gNuds/zFqVdVWuaEklJzxq287llmfB aWX69tgPhKSet68VYoyy3bY3+n//yjG9yfPQlYnhzxdBFJHcUoLbtKpn/Wp4ZrGb8B I5dn3GyX0K1eeoYzdM24D9E2HtBbMPp5Lwggo0Ao= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727722AbgC0DYV (ORCPT ); Thu, 26 Mar 2020 23:24:21 -0400 Received: from mail-lf1-f68.google.com ([209.85.167.68]:37790 "EHLO mail-lf1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726363AbgC0DYV (ORCPT ); Thu, 26 Mar 2020 23:24:21 -0400 Received: by mail-lf1-f68.google.com with SMTP id j11so6690297lfg.4 for ; Thu, 26 Mar 2020 20:24:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=WqlgEyg9y7uuAPxy577cVMUd3cF1yLpYiceQFIfBvp0=; b=eKUmY5/1JeJPIfRiVE1DqyubJzXLusIjTtIOS6QZI6Lxp260kF2xbps8bxKV5i+MPY P6vk0HgEvc9KiCOekc/QzuOAiSvHl52t43HSgbRPU9yqbegFMMIJGif51HsKr1vuTYRZ Uq+dwn7ljedT1tMdNmD+BHYa31ROiOUf/ycv8= 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=WqlgEyg9y7uuAPxy577cVMUd3cF1yLpYiceQFIfBvp0=; b=qy2U1h0zqVg60HzOLixyAMfWBs7SkhtAgrH0HDnfMsfpsq1/D0bEqG6pdNM9lDm/j3 t0AYuVOptgLGxiAa+D7emn5QuAxZYvUKQ2JSoID+s7vZdV2iPHsm9akPGTNN7ZOW0nBN Q5Vc2Auv50UNeXl7EnXAk7iRvR9ZEHQbwkWt+IERPB8TMyJeblfesnHFhQA/zabq2YBx tO49uV/xEOfI2ummkhuzBfe6DN9zRB32xmtVHG1W66sygzdWDz7VCA+syp9RD43GkiXM IRudtWgtuStrcD8Dkxf0FqtUa2hR86Bb/aOeZ4baHTfLmRlub1cPWKXyy0Lb7FFHLP5+ kudw== X-Gm-Message-State: ANhLgQ2dAthrYqAih7cHgkjqe1UWvH2p8ayhYRJXUxXyclxE809GjsuM gpMy/0mE9hKurzxyunA9wiE+Eap2to4= X-Google-Smtp-Source: ADFU+vt65/q9ZeYpkZHGx2/kmFd5lewNmQrOO/HxkjEOhAvaGl/HFY/zg3isvp+BUbP79dQB0+T/Hw== X-Received: by 2002:a19:88d4:: with SMTP id k203mr7663365lfd.75.1585279456761; Thu, 26 Mar 2020 20:24:16 -0700 (PDT) Received: from mail-lj1-f172.google.com (mail-lj1-f172.google.com. [209.85.208.172]) by smtp.gmail.com with ESMTPSA id m12sm2161482lji.50.2020.03.26.20.24.15 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Mar 2020 20:24:15 -0700 (PDT) Received: by mail-lj1-f172.google.com with SMTP id g12so8779606ljj.3 for ; Thu, 26 Mar 2020 20:24:15 -0700 (PDT) X-Received: by 2002:a2e:9b8e:: with SMTP id z14mr7111562lji.150.1585279455046; Thu, 26 Mar 2020 20:24:15 -0700 (PDT) MIME-Version: 1.0 References: <20200327022836.881203-1-viro@ZenIV.linux.org.uk> <20200327022836.881203-6-viro@ZenIV.linux.org.uk> In-Reply-To: <20200327022836.881203-6-viro@ZenIV.linux.org.uk> From: Linus Torvalds Date: Thu, 26 Mar 2020 20:23:59 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC][PATCH v2 6/8] x86: don't reload after cmpxchg in unsafe_atomic_op2() loop To: Al Viro Cc: Thomas Gleixner , "the arch/x86 maintainers" , Linux Kernel Mailing List 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 Thu, Mar 26, 2020 at 7:28 PM Al Viro wrote: > > From: Al Viro > > lock cmpxchg leaves the current value in eax; no need to reload it. I think this one is buggy. Patch edited to remove the "-" lines, so that you see the end result: > int oldval = 0, ret, tem; \ > asm volatile("1:\tmovl %2, %0\n" \ > + "2:\tmovl\t%0, %3\n" \ > "\t" insn "\n" \ > + "3:\t" LOCK_PREFIX "cmpxchgl %3, %2\n" \ > + "\tjnz\t2b\n" \ > + "4:\n" \ > "\t.section .fixup,\"ax\"\n" \ > + "5:\tmov\t%5, %1\n" \ > "\tjmp\t3b\n" \ > "\t.previous\n" \ > + _ASM_EXTABLE_UA(1b, 5b) \ > + _ASM_EXTABLE_UA(3b, 5b) \ > : "=&a" (oldval), "=&r" (ret), \ > "+m" (*uaddr), "=&r" (tem) \ > : "r" (oparg), "i" (-EFAULT), "1" (0)); \ I think that "\tjmp\t3b\n" line in the fixup section should be "\tjmp\t4b\n" because you don't want to jump to the cmpxchg instruction. Maybe I'm misreading it. Linus