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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD2C5C433F5 for ; Mon, 9 May 2022 03:20:13 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 209166B0071; Sun, 8 May 2022 23:20:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1B6EE6B0073; Sun, 8 May 2022 23:20:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 080656B0074; Sun, 8 May 2022 23:20:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id EDF246B0071 for ; Sun, 8 May 2022 23:20:12 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id C1C4660AD0 for ; Mon, 9 May 2022 03:20:12 +0000 (UTC) X-FDA: 79444751064.21.7BBD65D Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf13.hostedemail.com (Postfix) with ESMTP id 255C020063 for ; Mon, 9 May 2022 03:19:55 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KxRBL6CHkzXdpY; Mon, 9 May 2022 11:15:22 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 9 May 2022 11:20:07 +0800 Subject: Re: [PATCH v2 1/4] mm/migration: reduce the rcu lock duration To: "ying.huang@intel.com" , , CC: , , , , , , References: <20220425132723.34824-1-linmiaohe@huawei.com> <20220425132723.34824-2-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <43a1a61e-bffe-b995-0618-f2a02f17ab5a@huawei.com> Date: Mon, 9 May 2022 11:20:07 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Stat-Signature: 78peeb6ig4s7wy5tz4arjmp5dco4wt5s Authentication-Results: imf13.hostedemail.com; dkim=none; spf=pass (imf13.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 255C020063 X-HE-Tag: 1652066395-802884 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/5/6 11:23, ying.huang@intel.com wrote: > On Mon, 2022-04-25 at 21:27 +0800, Miaohe Lin wrote: >> rcu_read_lock is required by grabbing the task refcount but it's not >> needed for ptrace_may_access. So we could release the rcu lock after >> task refcount is successfully grabbed to reduce the rcu holding time. >> >> Reviewed-by: Muchun Song >> Reviewed-by: Christoph Hellwig >> Signed-off-by: Miaohe Lin >> Cc: Huang Ying >> Cc: David Howells >> Cc: Christoph Lameter >> --- >>  mm/migrate.c | 3 +-- >>  1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index b2678279eb43..b779646665fe 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1902,17 +1902,16 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) >>   return ERR_PTR(-ESRCH); >>   } >>   get_task_struct(task); >> + rcu_read_unlock(); >>   >> >>   /* >>   * Check if this process has the right to modify the specified >>   * process. Use the regular "ptrace_may_access()" checks. >>   */ >>   if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { >> - rcu_read_unlock(); >>   mm = ERR_PTR(-EPERM); >>   goto out; >>   } >> - rcu_read_unlock(); >>   >> >>   mm = ERR_PTR(security_task_movememory(task)); >>   if (IS_ERR(mm)) > > Hi, Miaohe, > > Please check the previous discussion and verify whether the original > reported race condition is stll valid by yourself before resending this > patch again. If you find that the original race condition isn't > possible now, please add the analysis in your change log. > Sorry for late respond. It's a pity that this change is still not verified by the relevant experts. I will try to give my analysis in my change log instead if the original race condition is invalid now. Many thanks! > Best Regards, > Huang, Ying > > . >