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 X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 B985AC433EB for ; Mon, 17 Aug 2020 22:10:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A17CD2063A for ; Mon, 17 Aug 2020 22:10:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387414AbgHQWKZ (ORCPT ); Mon, 17 Aug 2020 18:10:25 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:60230 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730157AbgHQWKG (ORCPT ); Mon, 17 Aug 2020 18:10:06 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1k7nKO-001qoV-OX; Mon, 17 Aug 2020 16:10:04 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.int.ebiederm.org) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1k7nKN-0004PB-S0; Mon, 17 Aug 2020 16:10:04 -0600 From: "Eric W. Biederman" To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, criu@openvz.org, bpf@vger.kernel.org, Linus Torvalds , Alexander Viro , Christian Brauner , Oleg Nesterov , Cyrill Gorcunov , Jann Horn , Kees Cook , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Jeff Layton , Miklos Szeredi , Matthew Wilcox , "J. Bruce Fields" , Matthew Wilcox , Trond Myklebust , Chris Wright , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , "Eric W. Biederman" Date: Mon, 17 Aug 2020 17:04:16 -0500 Message-Id: <20200817220425.9389-8-ebiederm@xmission.com> X-Mailer: git-send-email 2.25.0 In-Reply-To: <87ft8l6ic3.fsf@x220.int.ebiederm.org> References: <87ft8l6ic3.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-XM-SPF: eid=1k7nKN-0004PB-S0;;;mid=<20200817220425.9389-8-ebiederm@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+MSKEEDBeBw7dsl4MHrKCmLyi274gTksY= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH 08/17] proc/fd: In proc_fd_link use fcheck_task X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When discussing[1] exec and posix file locks it was realized that none of the callers of get_files_struct fundamentally needed to call get_files_struct, and that by switching them to helper functions instead it will both simplify their code and remove unnecessary increments of files_struct.count. Those unnecessary increments can result in exec unnecessarily unsharing files_struct which breaking posix locks, and it can result in fget_light having to fallback to fget reducing system performance. Using fcheck_task instead of get_files_struct simplifies proc_fd_link by removing unnecessary locking, and reference counting. [1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com Suggested-by: Oleg Nesterov Signed-off-by: "Eric W. Biederman" --- fs/proc/fd.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 4048a87c51ee..abfdcb21cc79 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -141,29 +141,23 @@ static const struct dentry_operations tid_fd_dentry_operations = { static int proc_fd_link(struct dentry *dentry, struct path *path) { - struct files_struct *files = NULL; struct task_struct *task; int ret = -ENOENT; task = get_proc_task(d_inode(dentry)); if (task) { - files = get_files_struct(task); - put_task_struct(task); - } - - if (files) { unsigned int fd = proc_fd(d_inode(dentry)); struct file *fd_file; - spin_lock(&files->file_lock); - fd_file = fcheck_files(files, fd); + rcu_read_lock(); + fd_file = fcheck_task(task, fd); if (fd_file) { *path = fd_file->f_path; path_get(&fd_file->f_path); ret = 0; } - spin_unlock(&files->file_lock); - put_files_struct(files); + rcu_read_unlock(); + put_task_struct(task); } return ret; -- 2.25.0