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 47E89CCA480 for ; Mon, 18 Jul 2022 00:33:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233083AbiGRAde (ORCPT ); Sun, 17 Jul 2022 20:33:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233098AbiGRAdJ (ORCPT ); Sun, 17 Jul 2022 20:33:09 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A113A13D3A for ; Sun, 17 Jul 2022 17:32:55 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 4E673B80EEA for ; Mon, 18 Jul 2022 00:32:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 03699C3411E; Mon, 18 Jul 2022 00:32:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1658104373; bh=ad9qU9+S8nrjzRSLgCWKeMO0ubiccEyrWVL0ep0w5gs=; h=Date:To:From:Subject:From; b=ojv8x1oEe6zVt89YyPxUmLeYNNJLIlZADZJzvbBIeX+SkmqDV+IWzzbOZk5pHRn7t yrTjl4OEI6/vvYiVqzGtB3ugstKC+51Kn683rgYcDm7esHHsHnzoxPw5RtkgBgHBwI bLnqswLTaAokK1VirSrNSdh/V6ifONUF1vkfwwOk= Date: Sun, 17 Jul 2022 17:32:52 -0700 To: mm-commits@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com, willy@infradead.org, viro@zeniv.linux.org.uk, kaleshsingh@google.com, ebiederm@xmission.com, bhe@redhat.com, bfoster@redhat.com, adobriyan@gmail.com, chengzhihao1@huawei.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-nonmm-stable] proc-fix-a-dentry-lock-race-between-release_task-and-lookup.patch removed from -mm tree Message-Id: <20220718003253.03699C3411E@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The quilt patch titled Subject: proc: fix a dentry lock race between release_task and lookup has been removed from the -mm tree. Its filename was proc-fix-a-dentry-lock-race-between-release_task-and-lookup.patch This patch was dropped because it was merged into the mm-nonmm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Zhihao Cheng Subject: proc: fix a dentry lock race between release_task and lookup Date: Wed, 13 Jul 2022 21:00:29 +0800 Commit 7bc3e6e55acf06 ("proc: Use a list of inodes to flush from proc") moved proc_flush_task() behind __exit_signal(). Then, process systemd can take long period high cpu usage during releasing task in following concurrent processes: systemd ps kernel_waitid stat(/proc/tgid) do_wait filename_lookup wait_consider_task lookup_fast release_task __exit_signal __unhash_process detach_pid __change_pid // remove task->pid_links d_revalidate -> pid_revalidate // 0 d_invalidate(/proc/tgid) shrink_dcache_parent(/proc/tgid) d_walk(/proc/tgid) spin_lock_nested(/proc/tgid/fd) // iterating opened fd proc_flush_pid | d_invalidate (/proc/tgid/fd) | shrink_dcache_parent(/proc/tgid/fd) | shrink_dentry_list(subdirs) ↓ shrink_lock_dentry(/proc/tgid/fd) --> race on dentry lock Function d_invalidate() will remove dentry from hash firstly, but why does proc_flush_pid() process dentry '/proc/tgid/fd' before dentry '/proc/tgid'? That's because proc_pid_make_inode() adds proc inode in reverse order by invoking hlist_add_head_rcu(). But proc should not add any inodes under '/proc/tgid' except '/proc/tgid/task/pid', fix it by adding inode into 'pid->inodes' only if the inode is /proc/tgid or /proc/tgid/task/pid. Performance regression: Create 200 tasks, each task open one file for 50,000 times. Kill all tasks when opened files exceed 10,000,000 (cat /proc/sys/fs/file-nr). Before fix: $ time killall -wq aa real 4m40.946s # During this period, we can see 'ps' and 'systemd' taking high cpu usage. After fix: $ time killall -wq aa real 1m20.732s # During this period, we can see 'systemd' taking high cpu usage. Link: https://lkml.kernel.org/r/20220713130029.4133533-1-chengzhihao1@huawei.com Fixes: 7bc3e6e55acf06 ("proc: Use a list of inodes to flush from proc") Link: https://bugzilla.kernel.org/show_bug.cgi?id=216054 Signed-off-by: Zhihao Cheng Signed-off-by: Zhang Yi Suggested-by: Brian Foster Reviewed-by: Brian Foster Cc: Al Viro Cc: Alexey Dobriyan Cc: Eric Biederman Cc: Matthew Wilcox Cc: Baoquan He Cc: Kalesh Singh Cc: Yu Kuai Signed-off-by: Andrew Morton --- fs/proc/base.c | 46 ++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 38 insertions(+), 8 deletions(-) --- a/fs/proc/base.c~proc-fix-a-dentry-lock-race-between-release_task-and-lookup +++ a/fs/proc/base.c @@ -1885,7 +1885,7 @@ void proc_pid_evict_inode(struct proc_in put_pid(pid); } -struct inode *proc_pid_make_inode(struct super_block * sb, +struct inode *proc_pid_make_inode(struct super_block *sb, struct task_struct *task, umode_t mode) { struct inode * inode; @@ -1914,11 +1914,6 @@ struct inode *proc_pid_make_inode(struct /* Let the pid remember us for quick removal */ ei->pid = pid; - if (S_ISDIR(mode)) { - spin_lock(&pid->lock); - hlist_add_head_rcu(&ei->sibling_inodes, &pid->inodes); - spin_unlock(&pid->lock); - } task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid); security_task_to_inode(task, inode); @@ -1931,6 +1926,39 @@ out_unlock: return NULL; } +/* + * Generating an inode and adding it into @pid->inodes, so that task will + * invalidate inode's dentry before being released. + * + * This helper is used for creating dir-type entries under '/proc' and + * '/proc//task'. Other entries(eg. fd, stat) under '/proc/' + * can be released by invalidating '/proc/' dentry. + * In theory, dentries under '/proc//task' can also be released by + * invalidating '/proc/' dentry, we reserve it to handle single + * thread exiting situation: Any one of threads should invalidate its + * '/proc//task/' dentry before released. + */ +static struct inode *proc_pid_make_base_inode(struct super_block *sb, + struct task_struct *task, umode_t mode) +{ + struct inode *inode; + struct proc_inode *ei; + struct pid *pid; + + inode = proc_pid_make_inode(sb, task, mode); + if (!inode) + return NULL; + + /* Let proc_flush_pid find this directory inode */ + ei = PROC_I(inode); + pid = ei->pid; + spin_lock(&pid->lock); + hlist_add_head_rcu(&ei->sibling_inodes, &pid->inodes); + spin_unlock(&pid->lock); + + return inode; +} + int pid_getattr(struct user_namespace *mnt_userns, const struct path *path, struct kstat *stat, u32 request_mask, unsigned int query_flags) { @@ -3369,7 +3397,8 @@ static struct dentry *proc_pid_instantia { struct inode *inode; - inode = proc_pid_make_inode(dentry->d_sb, task, S_IFDIR | S_IRUGO | S_IXUGO); + inode = proc_pid_make_base_inode(dentry->d_sb, task, + S_IFDIR | S_IRUGO | S_IXUGO); if (!inode) return ERR_PTR(-ENOENT); @@ -3671,7 +3700,8 @@ static struct dentry *proc_task_instanti struct task_struct *task, const void *ptr) { struct inode *inode; - inode = proc_pid_make_inode(dentry->d_sb, task, S_IFDIR | S_IRUGO | S_IXUGO); + inode = proc_pid_make_base_inode(dentry->d_sb, task, + S_IFDIR | S_IRUGO | S_IXUGO); if (!inode) return ERR_PTR(-ENOENT); _ Patches currently in -mm which might be from chengzhihao1@huawei.com are