From patchwork Sat May 16 03:46:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Shaokun Zhang X-Patchwork-Id: 1291823 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=hisilicon.com Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49PB8B4JMJz9s3x for ; Sat, 16 May 2020 13:48:26 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727898AbgEPDsU (ORCPT ); Fri, 15 May 2020 23:48:20 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:42620 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726247AbgEPDsU (ORCPT ); Fri, 15 May 2020 23:48:20 -0400 Received: from DGGEMS405-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id E748392A9D799AE0A1EB; Sat, 16 May 2020 11:48:16 +0800 (CST) Received: from localhost.localdomain (10.69.192.56) by DGGEMS405-HUB.china.huawei.com (10.3.19.205) with Microsoft SMTP Server id 14.3.487.0; Sat, 16 May 2020 11:48:10 +0800 From: Shaokun Zhang To: , CC: Yuqi Jin , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski , Jiri Pirko , Arvind Sankar , Peter Zijlstra , Eric Dumazet , Jiong Wang , Shaokun Zhang Subject: [PATCH v2] net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()" Date: Sat, 16 May 2020 11:46:49 +0800 Message-ID: <1589600809-18001-1-git-send-email-zhangshaokun@hisilicon.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 X-Originating-IP: [10.69.192.56] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Yuqi Jin Commit adb03115f459 ("net: get rid of an signed integer overflow in ip_idents_reserve()") used atomic_cmpxchg to replace "atomic_add_return" inside the function "ip_idents_reserve". The reason was to avoid UBSAN warning. However, this change has caused performance degrade and in GCC-8, fno-strict-overflow is now mapped to -fwrapv -fwrapv-pointer and signed integer overflow is now undefined by default at all optimization levels[1]. Moreover, it was a bug in UBSAN vs -fwrapv /-fno-strict-overflow, so Let's revert it safely. [1] https://gcc.gnu.org/gcc-8/changes.html Suggested-by: Peter Zijlstra Suggested-by: Eric Dumazet Cc: "David S. Miller" Cc: Alexey Kuznetsov Cc: Hideaki YOSHIFUJI Cc: Jakub Kicinski Cc: Jiri Pirko Cc: Arvind Sankar Cc: Peter Zijlstra Cc: Eric Dumazet Cc: Jiong Wang Signed-off-by: Yuqi Jin Signed-off-by: Shaokun Zhang --- ChangLog: * Revise the commit log * Add some comments. If it's wholly unnecessary, we can remove it. Patch v1: https://patchwork.ozlabs.org/project/netdev/patch/1579058620-26684-1-git-send-email-zhangshaokun@hisilicon.com/ net/ipv4/route.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 788c69d9bfe0..455871d6b3a0 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -491,18 +491,16 @@ u32 ip_idents_reserve(u32 hash, int segs) atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = READ_ONCE(*p_tstamp); u32 now = (u32)jiffies; - u32 new, delta = 0; + u32 delta = 0; if (old != now && cmpxchg(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); - /* Do not use atomic_add_return() as it makes UBSAN unhappy */ - do { - old = (u32)atomic_read(p_id); - new = old + delta + segs; - } while (atomic_cmpxchg(p_id, old, new) != old); - - return new - segs; + /* If UBSAN reports an error there, please make sure your compiler + * supports -fno-strict-overflow before reporting it that was a bug + * in UBSAN, and it has been fixed in GCC-8. + */ + return atomic_add_return(segs + delta, p_id) - segs; } EXPORT_SYMBOL(ip_idents_reserve);