From patchwork Wed May 25 08:18:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Miaohe Lin X-Patchwork-Id: 12860777 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 3A0CBC433F5 for ; Wed, 25 May 2022 08:18:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A8BD18D0005; Wed, 25 May 2022 04:18:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A38568D0003; Wed, 25 May 2022 04:18:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 902B08D0005; Wed, 25 May 2022 04:18:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 7ED268D0002 for ; Wed, 25 May 2022 04:18:17 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 55DA321036 for ; Wed, 25 May 2022 08:18:17 +0000 (UTC) X-FDA: 79503563034.27.61563B6 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf10.hostedemail.com (Postfix) with ESMTP id DEB59C0013 for ; Wed, 25 May 2022 08:17:39 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4L7P4x2CjJzQkMh; Wed, 25 May 2022 16:15:13 +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; Wed, 25 May 2022 16:18:13 +0800 From: Miaohe Lin To: , , CC: , , , , , , , , , , Subject: [PATCH v3 1/4] mm: reduce the rcu lock duration Date: Wed, 25 May 2022 16:18:19 +0800 Message-ID: <20220525081822.53547-2-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20220525081822.53547-1-linmiaohe@huawei.com> References: <20220525081822.53547-1-linmiaohe@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.175.124.27] 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-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DEB59C0013 X-Stat-Signature: 47uea43sfpbffz15qyrkugocxfg84qg5 Authentication-Results: imf10.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf10.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Rspam-User: X-HE-Tag: 1653466659-788344 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: 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 Signed-off-by: Miaohe Lin Cc: Huang Ying Cc: David Howells Cc: Christoph Lameter Reviewed-by: Oscar Salvador --- 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))