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=-11.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 32AFCC4161D for ; Thu, 11 Oct 2018 15:03:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D622C2075C for ; Thu, 11 Oct 2018 15:03:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="bIXGqRqW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D622C2075C Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.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 S1727329AbeJKWaf (ORCPT ); Thu, 11 Oct 2018 18:30:35 -0400 Received: from mail-it1-f196.google.com ([209.85.166.196]:38970 "EHLO mail-it1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726071AbeJKWae (ORCPT ); Thu, 11 Oct 2018 18:30:34 -0400 Received: by mail-it1-f196.google.com with SMTP id w200-v6so13607109itc.4 for ; Thu, 11 Oct 2018 08:03:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=H/naWTO9CxdQZFOUKhonf+vvaQc+Kk2l6u9PJleafIc=; b=bIXGqRqWCR390AsBDOCm/n203ueETsQv8ljH42z4AdpWiVv9E1I2j5yHWZTSiOi+yn 37aiTc7P4zIMpcAfQp0xi3IBQvu/4upkwywY5dydqbnC8xD3A0SbvQhxKceMirE4UD6D y7PVkjv3/oyZlwjRb1kJlafzC/mIDBqinxRpTfzVtK63NpTtSPixrP8kqpk/yRtku4TK 4ldYz1wSsl3JbAbivCBI8U1SWWW/YeszX6vpJpVuOTBCbkDiBcxUJv9tBptg9fMg8IYi eJMU5mQ9PVq6I+E2YA1JDZEf4ejo4fITbFysM0xI80bP6IMNAK7u9N6AHEfL0F+tu7l0 CaYg== 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=H/naWTO9CxdQZFOUKhonf+vvaQc+Kk2l6u9PJleafIc=; b=C26fqxRwUdUJyXfgSgJw/00R7pgXnXLURfciHlfY0i6ArMOKATnRIT9yKqCwWxoTGC KiwPvWkuVt920HdjYP4V03GktClLWKH1nsFp9aWoGL/x+Fr803WK3TZ/i+OwvXVETGM2 2U++71d6FdKWqiHygUk4GExu6G6Bvn+NkanrTq6IyaoPjIDLnWQ0Qz7pS2P364vkqQS3 TAXFeZzkO1JoNbJnxwqwYNtB/USrSBacztoOgHU3YR7A6uRQnH4V3nRMdAj9I03z+/XU d6U7IG/WYRb/BOOnu4Y8TXrVT25uXI7XwJPvEw0lnAuwiC+X9vlkuAqAB2q2h5ZftFu2 GvUg== X-Gm-Message-State: ABuFfojtrNpyLIMzCzzcy7lCUPuADZUUbCyl6zebs+yyj/jWYMrQNu9b AZogbs9qVciEFve0BE+NCGfqCRDdmJfXzbmKKutxTg== X-Google-Smtp-Source: ACcGV60Q0Sni2OQaONE4FxcT6rBUuISZnFyUv69/YifnU1DsU7jYB2ntUPPioRbyLgN8l4NMuFNk0cS3zxK6kv/MkyM= X-Received: by 2002:a24:f803:: with SMTP id a3-v6mr1596175ith.178.1539270180852; Thu, 11 Oct 2018 08:03:00 -0700 (PDT) MIME-Version: 1.0 References: <20181011103825.023036082@infradead.org> <20181011104019.748208519@infradead.org> In-Reply-To: <20181011104019.748208519@infradead.org> From: Eric Dumazet Date: Thu, 11 Oct 2018 08:02:48 -0700 Message-ID: Subject: Re: [PATCH 2/2] x86/percpu: Fix this_cpu_read() To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , LKML , "H. Peter Anvin" , Eric Dumazet , Borislav Petkov 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, Oct 11, 2018 at 3:45 AM Peter Zijlstra wrote: > > Eric reported that a sequence count loop using this_cpu_read() got > optimized out. This is wrong, this_cpu_read() must imply READ_ONCE() > because the interface is IRQ-safe, therefore an interrupt can have > changed the per-cpu value. > > Fixes: 59eaef78bfea ("x86/tsc: Remodel cyc2ns to use seqcount_latch()") > Reported-by: Eric Dumazet > Signed-off-by: Peter Zijlstra (Intel) Acked-by: Eric Dumazet > --- > arch/x86/include/asm/percpu.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > --- a/arch/x86/include/asm/percpu.h > +++ b/arch/x86/include/asm/percpu.h > @@ -185,22 +185,22 @@ do { \ > typeof(var) pfo_ret__; \ > switch (sizeof(var)) { \ > case 1: \ > - asm(op "b "__percpu_arg(1)",%0" \ > + asm volatile(op "b "__percpu_arg(1)",%0"\ > : "=q" (pfo_ret__) \ > : "m" (var)); \ > break; \ > case 2: \ > - asm(op "w "__percpu_arg(1)",%0" \ > + asm volatile(op "w "__percpu_arg(1)",%0"\ > : "=r" (pfo_ret__) \ > : "m" (var)); \ > break; \ > case 4: \ > - asm(op "l "__percpu_arg(1)",%0" \ > + asm volatile(op "l "__percpu_arg(1)",%0"\ > : "=r" (pfo_ret__) \ > : "m" (var)); \ > break; \ > case 8: \ > - asm(op "q "__percpu_arg(1)",%0" \ > + asm volatile(op "q "__percpu_arg(1)",%0"\ > : "=r" (pfo_ret__) \ > : "m" (var)); \ > break; \ > >