From patchwork Tue Apr 28 12:18:01 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: 11514393 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 1214F15AB for ; Tue, 28 Apr 2020 12:21:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02A9A2075E for ; Tue, 28 Apr 2020 12:21:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726841AbgD1MVS (ORCPT ); Tue, 28 Apr 2020 08:21:18 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:52726 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726645AbgD1MVR (ORCPT ); Tue, 28 Apr 2020 08:21:17 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jTPEi-0006os-K2; Tue, 28 Apr 2020 06:21:16 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jTPEh-0001LA-S1; Tue, 28 Apr 2020 06:21:16 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Linus Torvalds Cc: LKML , Linux FS Devel , Alexey Dobriyan , Alexey Gladkov , Andrew Morton , Alexey Gladkov , Oleg Nesterov , Thomas Gleixner , "Paul E. McKenney" References: <20200419141057.621356-1-gladkov.alexey@gmail.com> <87ftcv1nqe.fsf@x220.int.ebiederm.org> <87wo66vvnm.fsf_-_@x220.int.ebiederm.org> <20200424173927.GB26802@redhat.com> <87mu6ymkea.fsf_-_@x220.int.ebiederm.org> <875zdmmj4y.fsf_-_@x220.int.ebiederm.org> <878sihgfzh.fsf@x220.int.ebiederm.org> <87sggnajpv.fsf_-_@x220.int.ebiederm.org> Date: Tue, 28 Apr 2020 07:18:01 -0500 In-Reply-To: <87sggnajpv.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Tue, 28 Apr 2020 07:16:44 -0500") Message-ID: <87mu6vajnq.fsf_-_@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1jTPEh-0001LA-S1;;;mid=<87mu6vajnq.fsf_-_@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+Anr6qsqTLzFB5xXd0dlDeNH9ArfARscA= 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 sa07.xmission.com X-Spam-Level: X-Spam-Status: No, score=0.3 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,T_TooManySym_01,XMGappySubj_01 autolearn=disabled version=3.4.2 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] * 0.5 XMGappySubj_01 Very gappy subject * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa07 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Linus Torvalds X-Spam-Relay-Country: X-Spam-Timing: total 330 ms - load_scoreonly_sql: 0.04 (0.0%), signal_user_changed: 11 (3.3%), b_tie_ro: 10 (2.9%), parse: 0.87 (0.3%), extract_message_metadata: 11 (3.2%), get_uri_detail_list: 1.12 (0.3%), tests_pri_-1000: 14 (4.1%), tests_pri_-950: 1.24 (0.4%), tests_pri_-900: 1.00 (0.3%), tests_pri_-90: 87 (26.4%), check_bayes: 86 (25.9%), b_tokenize: 7 (2.0%), b_tok_get_all: 6 (1.7%), b_comp_prob: 1.80 (0.5%), b_tok_touch_all: 69 (20.8%), b_finish: 0.86 (0.3%), tests_pri_0: 190 (57.4%), check_dkim_signature: 0.54 (0.2%), check_dkim_adsp: 2.5 (0.8%), poll_dns_idle: 0.71 (0.2%), tests_pri_10: 3.2 (1.0%), tests_pri_500: 9 (2.8%), rewrite_mail: 0.00 (0.0%) Subject: [PATCH v4 1/2] rculist: Add hlists_swap_heads_rcu 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 Using the struct pid to refer to two tasks in de_thread was a clever idea and ultimately too clever, as it has lead to proc_flush_task being called inconsistently. To support rectifying this add hlists_swap_heads_rcu. An hlist primitive that just swaps the hlist heads of two lists. This is exactly what is needed for exchanging the pids of two tasks. Only consideration of correctness of the code has been given, as the caller is expected to be a slowpath. Signed-off-by: "Eric W. Biederman" --- include/linux/rculist.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 8214cdc715f2..67867e0d4cec 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -506,6 +506,27 @@ static inline void hlist_replace_rcu(struct hlist_node *old, WRITE_ONCE(old->pprev, LIST_POISON2); } +/** + * hlists_swap_heads_rcu - swap the lists the hlist heads point to + * @left: The hlist head on the left + * @right: The hlist head on the right + * + * The lists start out as [@left ][node1 ... ] and + [@right ][node2 ... ] + * The lists end up as [@left ][node2 ... ] + * [@right ][node1 ... ] + */ +static inline void hlists_swap_heads_rcu(struct hlist_head *left, struct hlist_head *right) +{ + struct hlist_node *node1 = left->first; + struct hlist_node *node2 = right->first; + + rcu_assign_pointer(left->first, node2); + rcu_assign_pointer(right->first, node1); + WRITE_ONCE(node2->pprev, &left->first); + WRITE_ONCE(node1->pprev, &right->first); +} + /* * return the first or the next element in an RCU protected hlist */