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 E8BE5CE79CC for ; Wed, 20 Sep 2023 11:12:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231593AbjITLMH (ORCPT ); Wed, 20 Sep 2023 07:12:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233970AbjITLMG (ORCPT ); Wed, 20 Sep 2023 07:12:06 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7A262C2; Wed, 20 Sep 2023 04:12:00 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97A12C433C7; Wed, 20 Sep 2023 11:11:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1695208320; bh=uHc4UgrN4XzoKh+DGF1PQDJ1c4JYNlGD5zoJ/jU3kDU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EwXGJYWnSHSBpKSFpLRbmdPXk99ikPurTLFEfQ+M+ZLK1VFlSNbhCnZ4rla+gvNfI i+l0nhxQCLJEpL28IZL2HcPXHYxnM1n7RLlAMcKyCauZMpChodHq2LKVvUjhIBcIOO fEinuKB8rxps4rQ2sL+gqnxUu9AuJlnoqJq808N4= Date: Wed, 20 Sep 2023 13:11:57 +0200 From: Greg KH To: Suraj Jitindar Singh Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org, adobriyan@gmail.com, sjitindarsingh@gmail.com, Zhihao Cheng , Zhang Yi , Brian Foster , Al Viro , Eric Biederman , Matthew Wilcox , Baoquan He , Kalesh Singh , Yu Kuai , Andrew Morton Subject: Re: [PATCH stable 5.10.y] proc: fix a dentry lock race between release_task and lookup Message-ID: <2023092048-posting-unlit-4734@gregkh> References: <20230919233335.170835-1-surajjs@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230919233335.170835-1-surajjs@amazon.com> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Sep 19, 2023 at 04:33:35PM -0700, Suraj Jitindar Singh wrote: > From: Zhihao Cheng > > commit d919a1e79bac890421537cf02ae773007bf55e6b upstream. > > 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 > [ bp: Context adjustments ] > Signed-off-by: Suraj Jitindar Singh both now queued up, thanks. greg k-h