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 7D1B3C433F5 for ; Mon, 30 May 2022 11:30:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235838AbiE3Lag (ORCPT ); Mon, 30 May 2022 07:30:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39666 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235780AbiE3LaK (ORCPT ); Mon, 30 May 2022 07:30:10 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 322187E1F9 for ; Mon, 30 May 2022 04:30:09 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LBY8D0zVZzcfX2; Mon, 30 May 2022 19:29:00 +0800 (CST) Received: from huawei.com (10.175.124.27) 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, 30 May 2022 19:30:06 +0800 From: Miaohe Lin To: , CC: , , , , , , , , , , , Subject: [PATCH v4 1/4] mm: reduce the rcu lock duration Date: Mon, 30 May 2022 19:30:13 +0800 Message-ID: <20220530113016.16663-2-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20220530113016.16663-1-linmiaohe@huawei.com> References: <20220530113016.16663-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.124.27] 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 Commit 3268c63eded4 ("mm: fix move/migrate_pages() race on task struct") extends the period of the rcu_read_lock until after the permissions checks are done to prevent the task pointed to from changing from under us. But the task_struct refcount is also taken at that time, the reference to task is guaranteed to be stable. So it's unnecessary to extend the period of the rcu_read_lock. Release the rcu lock after task refcount is successfully grabbed to reduce the rcu holding time. Reviewed-by: Muchun Song Reviewed-by: Christoph Hellwig Reviewed-by: Oscar Salvador Signed-off-by: Miaohe Lin Cc: Huang Ying Cc: David Howells Cc: Christoph Lameter --- mm/mempolicy.c | 3 +-- mm/migrate.c | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 0b4ba3ee810e..2dad094177bf 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1609,6 +1609,7 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode, goto out; } get_task_struct(task); + rcu_read_unlock(); err = -EINVAL; @@ -1617,11 +1618,9 @@ static int kernel_migrate_pages(pid_t pid, unsigned long maxnode, * Use the regular "ptrace_may_access()" checks. */ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { - rcu_read_unlock(); err = -EPERM; goto out_put; } - rcu_read_unlock(); task_nodes = cpuset_mems_allowed(task); /* Is the user allowed to access the target nodes? */ diff --git a/mm/migrate.c b/mm/migrate.c index e51588e95f57..e88ebb88fa6f 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)) -- 2.23.0