From mboxrd@z Thu Jan 1 00:00:00 1970 From: gfree.wind@foxmail.com Subject: [PATCH net-next 1/1] tcp: sysctl: Fix a race to avoid unexpected 0 window from space Date: Fri, 24 Mar 2017 07:05:12 +0800 Message-ID: <1490310312-20661-1-git-send-email-gfree.wind@foxmail.com> Cc: Gao Feng To: davem@davemloft.net, netdev@vger.kernel.org, gfree.wind@foxmail.com Return-path: Received: from smtpbgsg2.qq.com ([54.254.200.128]:42451 "EHLO smtpbgsg2.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752008AbdCWXF2 (ORCPT ); Thu, 23 Mar 2017 19:05:28 -0400 Sender: netdev-owner@vger.kernel.org List-ID: From: Gao Feng Because sysctl_tcp_adv_win_scale could be changed any time, so there is one race in tcp_win_from_space. For example, 1.sysctl_tcp_adv_win_scale<=0 (sysctl_tcp_adv_win_scale is negative now) 2.space>>(-sysctl_tcp_adv_win_scale) (sysctl_tcp_adv_win_scale is postive now) As a result, tcp_win_from_space returns 0. It is unexpected. Certainly if the compiler put the sysctl_tcp_adv_win_scale into one register firstly, then use the register directly, it would be ok. But we could not depend on the compiler behavior. Signed-off-by: Gao Feng --- include/net/tcp.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 6ec4ea6..119b592 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1252,9 +1252,11 @@ void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd, static inline int tcp_win_from_space(int space) { - return sysctl_tcp_adv_win_scale<=0 ? - (space>>(-sysctl_tcp_adv_win_scale)) : - space - (space>>sysctl_tcp_adv_win_scale); + int tcp_adv_win_scale = sysctl_tcp_adv_win_scale; + + return tcp_adv_win_scale <= 0 ? + (space>>(-tcp_adv_win_scale)) : + space - (space>>tcp_adv_win_scale); } /* Note: caller must be prepared to deal with negative returns */ -- 1.9.1