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=-3.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 3BA5AC65BAF for ; Sun, 9 Dec 2018 22:20:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CA1C20661 for ; Sun, 9 Dec 2018 22:20:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0CA1C20661 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk 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 S1727968AbeLIWUg (ORCPT ); Sun, 9 Dec 2018 17:20:36 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35406 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726549AbeLIVzY (ORCPT ); Sun, 9 Dec 2018 16:55:24 -0500 Received: from pub.yeoldevic.com ([81.174.156.145] helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1gW72n-0002io-Sg; Sun, 09 Dec 2018 21:55:22 +0000 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gW72l-0003gY-8b; Sun, 09 Dec 2018 21:55:19 +0000 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , bp@alien8.de, "Peter Zijlstra" , "Thomas Gleixner" , eric.dumazet@gmail.com, hpa@zytor.com Date: Sun, 09 Dec 2018 21:50:33 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 311/328] x86/percpu: Fix this_cpu_read() In-Reply-To: X-SA-Exim-Connect-IP: 81.174.156.145 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.62-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra commit b59167ac7bafd804c91e49ad53c6d33a7394d4c8 upstream. 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: 7c3576d261ce ("[PATCH] i386: Convert PDA into the percpu section") Reported-by: Eric Dumazet Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Acked-by: Eric Dumazet Cc: hpa@zytor.com Cc: eric.dumazet@gmail.com Cc: bp@alien8.de Link: https://lkml.kernel.org/r/20181011104019.748208519@infradead.org [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- 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__) \ : constraint); \ break; \ case 2: \ - asm(op "w "__percpu_arg(1)",%0" \ + asm volatile(op "w "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : constraint); \ break; \ case 4: \ - asm(op "l "__percpu_arg(1)",%0" \ + asm volatile(op "l "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : constraint); \ break; \ case 8: \ - asm(op "q "__percpu_arg(1)",%0" \ + asm volatile(op "q "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : constraint); \ break; \