From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id AD28B6B0007 for ; Wed, 18 Apr 2018 14:57:01 -0400 (EDT) Received: by mail-pl0-f71.google.com with SMTP id 35-v6so1471462pla.18 for ; Wed, 18 Apr 2018 11:57:01 -0700 (PDT) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id z24si1503785pgn.55.2018.04.18.11.56.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 18 Apr 2018 11:57:00 -0700 (PDT) From: Yang Shi Subject: [PATCH -mmotm] prctl: add comment about mmap_sem and arg_lock Date: Thu, 19 Apr 2018 02:56:39 +0800 Message-Id: <1524077799-80690-1-git-send-email-yang.shi@linux.alibaba.com> Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@kernel.org, gorcunov@gmail.com, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Add comment to elaborate why mmap_sem for is used by prctl. Signed-off-by: Yang Shi --- akpm: this patch can be foled into: mm-introduce-arg_lock-to-protect-arg_startend-and-env_startend-in-mm_struct.patch kernel/sys.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sys.c b/kernel/sys.c index 0cc5a1c..943fdc5 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2011,6 +2011,10 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data return error; } + /* + * arg_lock protects concurent updates but we still need mmap_sem for + * read to exclude races with sys_brk. + */ down_read(&mm->mmap_sem); /* -- 1.8.3.1