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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC6B8C433FE for ; Tue, 24 May 2022 12:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237387AbiEXMg5 (ORCPT ); Tue, 24 May 2022 08:36:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58886 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234396AbiEXMg4 (ORCPT ); Tue, 24 May 2022 08:36:56 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 334A955202 for ; Tue, 24 May 2022 05:36:55 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4L6tss54HDzQkFP; Tue, 24 May 2022 20:33:53 +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; Tue, 24 May 2022 20:36:52 +0800 Subject: Re: [PATCH v2 1/4] mm/migration: reduce the rcu lock duration To: David Hildenbrand CC: , , , , , , , , References: <20220425132723.34824-1-linmiaohe@huawei.com> <20220425132723.34824-2-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <794b30f7-eea4-d254-9c1e-2fcd8a6aa16a@huawei.com> Date: Tue, 24 May 2022 20:36:52 +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: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/4/29 17:54, David Hildenbrand wrote: > On 25.04.22 15:27, 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)) > > Similar pattern in: > > mm/mempolicy.c:kernel_migrate_pages() > kernel/futex/syscalls.c:get_robust_list() > kernel/nsproxy.c:validate_nsset() > > Exception: > > sched/core_sched.c:sched_core_share_pid() > > > Should we unify -- i.e., adjust the remaining 3 as well? > I verified that this code change applies to kernel_migrate_pages(), but not get_robust_list() and validate_nsset(). It's because task_struct reference is not grabbed for later ones. Will send the new patch soon. Thanks!