From patchwork Mon Aug 17 22:04:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 11719437 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7F9B8618 for ; Mon, 17 Aug 2020 22:10:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6FED02072E for ; Mon, 17 Aug 2020 22:10:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730173AbgHQWKL (ORCPT ); Mon, 17 Aug 2020 18:10:11 -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?Da?= =?utf-8?q?niel_P=2E_Berrang=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 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 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa03.xmission.com X-Spam-Level: * X-Spam-Status: No, score=1.3 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,T_TooManySym_01,XMNoVowels autolearn=disabled version=3.4.2 X-Spam-Virus: No X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * 1.5 XMNoVowels Alpha-numberic number with no vowels * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 0; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: ; sa03 0; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: *;linux-kernel@vger.kernel.org X-Spam-Relay-Country: X-Spam-Timing: total 530 ms - load_scoreonly_sql: 0.02 (0.0%), signal_user_changed: 3.3 (0.6%), b_tie_ro: 2.3 (0.4%), parse: 0.74 (0.1%), extract_message_metadata: 8 (1.6%), get_uri_detail_list: 1.04 (0.2%), tests_pri_-1000: 10 (2.0%), tests_pri_-950: 0.89 (0.2%), tests_pri_-900: 0.78 (0.1%), tests_pri_-90: 256 (48.3%), check_bayes: 255 (48.1%), b_tokenize: 6 (1.2%), b_tok_get_all: 7 (1.3%), b_comp_prob: 1.59 (0.3%), b_tok_touch_all: 237 (44.8%), b_finish: 0.77 (0.1%), tests_pri_0: 241 (45.4%), check_dkim_signature: 0.36 (0.1%), check_dkim_adsp: 2.0 (0.4%), poll_dns_idle: 0.77 (0.1%), tests_pri_10: 1.71 (0.3%), tests_pri_500: 5 (1.0%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH 08/17] proc/fd: In proc_fd_link use fcheck_task X-Spam-Flag: No 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-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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" Acked-by: Christian Brauner --- 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;