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 A86E3C433EF for ; Mon, 9 May 2022 03:14:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1BFCD6B0071; Sun, 8 May 2022 23:14:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1499B6B0073; Sun, 8 May 2022 23:14:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F2A8B6B0074; Sun, 8 May 2022 23:14:38 -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 DFD976B0071 for ; Sun, 8 May 2022 23:14:38 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id AD8B0303ED for ; Mon, 9 May 2022 03:14:38 +0000 (UTC) X-FDA: 79444737036.14.6F96B37 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf02.hostedemail.com (Postfix) with ESMTP id 1FC0A80074 for ; Mon, 9 May 2022 03:14:30 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4KxR681W45zGpPt; Mon, 9 May 2022 11:11:44 +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 11:14:30 +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: <3cf42a6e-c13d-341d-00a0-876a61794273@huawei.com> Date: Mon, 9 May 2022 11:14:30 +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: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Authentication-Results: imf02.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf02.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 1FC0A80074 X-Rspam-User: X-Stat-Signature: gwyef4e4tdx5odc7do71k4c7gwanhcx4 X-HE-Tag: 1652066070-54515 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 2022/4/29 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? > Sorry for late respond. I think it's fine to do all of this together. But this patch is indeed under verifying now. I will try to do that after verified. Thanks!