From patchwork Mon Jan 4 23:21:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stephen Brennan X-Patchwork-Id: 11997761 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4229EC433E0 for ; Mon, 4 Jan 2021 23:24:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 156792253A for ; Mon, 4 Jan 2021 23:24:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727379AbhADXXC (ORCPT ); Mon, 4 Jan 2021 18:23:02 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:45114 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726333AbhADXXB (ORCPT ); Mon, 4 Jan 2021 18:23:01 -0500 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 104NIkN0157881; Mon, 4 Jan 2021 23:22:00 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : mime-version : content-transfer-encoding; s=corp-2020-01-29; bh=of7cDloEGBPE5l8WJ889ZLzwlRrbg724FmM0fBM4+OA=; b=GtFrS5/8a9nCTxCjnqVUQa91ZYBEEcVT1X9IWYtCbZXrYMFyvDIpjUQYBht/DXkgUWPF a4k+J08vTkAqjqEY4HeAN76GhVnFDhG2aTfE1qvd3vzixnYWwbFB1uoqPPPtyBtSoujn WLsdwkiDm2K5lx2/XwbJFtLEaD618jhsVxPR4ube9ECoiVwdkG65fZGMK1qubGijhkuP DrMO7GOv7KiWQWjZkI4K9VqP39aIT1uYIyEq6DYZOZ9lZ+Y8OZV7VW2fDj/WzY6Sy24+ eAl7Dw6QC5N9/geVG0wgcRV7HxE3FUByL1IZUDai2c0i6gkR5SIfwKcNPP82BMgP2BY5 fw== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by aserp2130.oracle.com with ESMTP id 35tebappcg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 04 Jan 2021 23:22:00 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 104NKJmP089224; Mon, 4 Jan 2021 23:21:59 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3020.oracle.com with ESMTP id 35uxnrut8r-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 04 Jan 2021 23:21:59 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 104NLq9j000985; Mon, 4 Jan 2021 23:21:54 GMT Received: from localhost (/10.159.240.116) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 04 Jan 2021 23:21:52 +0000 From: Stephen Brennan To: Alexey Dobriyan Cc: Stephen Brennan , James Morris , "Serge E. Hallyn" , linux-security-module@vger.kernel.org, Paul Moore , Stephen Smalley , Eric Paris , selinux@vger.kernel.org, Casey Schaufler , Eric Biederman , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Wilcox Subject: [PATCH v4] proc: Allow pid_revalidate() during LOOKUP_RCU Date: Mon, 4 Jan 2021 15:21:22 -0800 Message-Id: <20210104232123.31378-1-stephen.s.brennan@oracle.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9854 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 phishscore=0 spamscore=0 malwarescore=0 mlxscore=0 mlxlogscore=999 suspectscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101040141 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9854 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 phishscore=0 priorityscore=1501 spamscore=0 mlxscore=0 clxscore=1015 bulkscore=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101040141 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The pid_revalidate() function drops from RCU into REF lookup mode. When many threads are resolving paths within /proc in parallel, this can result in heavy spinlock contention on d_lockref as each thread tries to grab a reference to the /proc dentry (and drop it shortly thereafter). Investigation indicates that it is not necessary to drop RCU in pid_revalidate(), as no RCU data is modified and the function never sleeps. So, remove the LOOKUP_RCU check. Signed-off-by: Stephen Brennan Signed-off-by: Al Viro --- When running running ~100 parallel instances of "TZ=/etc/localtime ps -fe >/dev/null" on a 100CPU machine, the %sys utilization reaches 90%, and perf shows the following code path as being responsible for heavy contention on the d_lockref spinlock: walk_component() lookup_fast() d_revalidate() pid_revalidate() // returns -ECHILD unlazy_child() lockref_get_not_dead(&nd->path.dentry->d_lockref) <-- contention By applying this patch, %sys utilization falls to around 60% under the same workload. Although this particular workload is a bit contrived, we have seen some monitoring scripts which produced similarly high %sys time due to this contention. Changes in v4: - Simplify by unconditionally calling pid_update_inode() from pid_revalidate, and removing the LOOKUP_RCU check. Changes in v3: - Rather than call pid_update_inode() with flags, create proc_inode_needs_update() to determine whether the call can be skipped. - Restore the call to the security hook (see next patch). Changes in v2: - Remove get_pid_task_rcu_user() and get_proc_task_rcu(), since they were unnecessary. - Remove the call to security_task_to_inode(). fs/proc/base.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index f52217f432bc..633ef74e8dfd 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1974,19 +1974,18 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags) { struct inode *inode; struct task_struct *task; + int ret = 0; - if (flags & LOOKUP_RCU) - return -ECHILD; - - inode = d_inode(dentry); - task = get_proc_task(inode); + rcu_read_lock(); + inode = d_inode_rcu(dentry); + task = pid_task(proc_pid(inode), PIDTYPE_PID); if (task) { pid_update_inode(task, inode); - put_task_struct(task); - return 1; + ret = 1; } - return 0; + rcu_read_unlock(); + return ret; } static inline bool proc_inode_is_dead(struct inode *inode)