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=-7.5 required=3.0 tests=DATE_IN_PAST_06_12, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 3BECFC17440 for ; Sun, 10 Nov 2019 00:56:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 110E720B7C for ; Sun, 10 Nov 2019 00:56:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573347416; bh=BUdFQb1kZQPx4ojrvJZEsGbT37KVn2Olmo5PxzNJ0ts=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=I8lGbfBXlUCokZZzcICIq6E+N4/djbn0XsKFtRS07PemLUuXPBA2bKbc2sjm5pHnp jK2PdsaDlU9eOsATrDfsddy9GUTRIAplaXmMbt5toUOUT0rYnvBIdcVQb0oYTb2M2x WIKQb0JMsE91jVDe7j945KxqHyev9ihXyqnTdxAA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726587AbfKJA42 (ORCPT ); Sat, 9 Nov 2019 19:56:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:38758 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726470AbfKJA41 (ORCPT ); Sat, 9 Nov 2019 19:56:27 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [216.9.110.3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5E38220B7C; Sun, 10 Nov 2019 00:56:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573347386; bh=BUdFQb1kZQPx4ojrvJZEsGbT37KVn2Olmo5PxzNJ0ts=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=CkiMgTTcMrqVeCCUu1Ej0COoXnMBxb150kdeBXTLRvzn0Ww6G59cnIxi9rEeKYYFr GlydRKlKIdFq+qyHJ6m8cSCaeoxHvoAB/mk3P5WrSiCYTgfeIPoAbwnOBCrDdtnHt5 hQu8wfiCv2tV7iKzEDcUQ/6lr/mTlc9bwQ1GD02w= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id BE053352280C; Sat, 9 Nov 2019 10:53:36 -0800 (PST) Date: Sat, 9 Nov 2019 10:53:36 -0800 From: "Paul E. McKenney" To: Eric Dumazet Cc: Thomas Gleixner , linux-kernel , Eric Dumazet Subject: Re: [PATCH 1/2] list: add hlist_unhashed_lockless() Message-ID: <20191109185336.GA19013@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191107193738.195914-1-edumazet@google.com> <20191108192448.GB20975@paulmck-ThinkPad-P72> <20191108234224.GF20975@paulmck-ThinkPad-P72> <20191109175440.GJ20975@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191109175440.GJ20975@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 09, 2019 at 09:54:40AM -0800, Paul E. McKenney wrote: > On Fri, Nov 08, 2019 at 07:15:16PM -0800, Eric Dumazet wrote: > > On Fri, Nov 8, 2019 at 3:42 PM Paul E. McKenney wrote: > > > > > > On Fri, Nov 08, 2019 at 12:17:49PM -0800, Eric Dumazet wrote: > > > > On Fri, Nov 8, 2019 at 11:24 AM Paul E. McKenney wrote: > > > > > > > > > > On Thu, Nov 07, 2019 at 11:37:37AM -0800, Eric Dumazet wrote: > > > > > > We would like to use hlist_unhashed() from timer_pending(), > > > > > > which runs without protection of a lock. > > > > > > > > > > > > Note that other callers might also want to use this variant. > > > > > > > > > > > > Instead of forcing a READ_ONCE() for all hlist_unhashed() > > > > > > callers, add a new helper with an explicit _lockless suffix > > > > > > in the name to better document what is going on. > > > > > > > > > > > > Also add various WRITE_ONCE() in __hlist_del(), hlist_add_head() > > > > > > and hlist_add_before()/hlist_add_behind() to pair with > > > > > > the READ_ONCE(). > > > > > > > > > > > > Signed-off-by: Eric Dumazet > > > > > > Cc: "Paul E. McKenney" > > > > > > Cc: Thomas Gleixner > > > > > > > > > > I have queued this, but if you prefer it go some other way: > > > > > > > > > > Acked-by: Paul E. McKenney > > > > > > > > > > But shouldn't the uses in include/linux/rculist.h also be converted > > > > > into the patch below? If so, I will squash the following into your > > > > > patch. > > > > > > > > > > Thanx, Paul > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > Agreed, thanks for the addition of this Paul. > > > > > > Very good, squashed and pushed, thank you! > > > > > > > I have another KCSAN report of a bug that will force us to use > > hlist_unhashed_lockless() from sk_unhashed() > > > > (Meaning we also need to add some WRITE_ONCE() annotations to > > include/linux/list_nulls.h ) > > > > BUG: KCSAN: data-race in inet_unhash / inet_unhash > > > > write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1: > > __hlist_nulls_del include/linux/list_nulls.h:88 [inline] > > hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline] > > __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline] > > inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612 > > tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249 > > tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854 > > tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56 > > tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479 > > tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599 > > tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619 > > call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404 > > expire_timers kernel/time/timer.c:1449 [inline] > > __run_timers kernel/time/timer.c:1773 [inline] > > __run_timers kernel/time/timer.c:1740 [inline] > > run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786 > > __do_softirq+0x115/0x33f kernel/softirq.c:292 > > invoke_softirq kernel/softirq.c:373 [inline] > > irq_exit+0xbb/0xe0 kernel/softirq.c:413 > > exiting_irq arch/x86/include/asm/apic.h:536 [inline] > > smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137 > > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830 > > native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71 > > arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571 > > default_idle_call+0x1e/0x40 kernel/sched/idle.c:94 > > cpuidle_idle_call kernel/sched/idle.c:154 [inline] > > do_idle+0x1af/0x280 kernel/sched/idle.c:263 > > cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355 > > start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264 > > secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241 > > > > read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0: > > sk_unhashed include/net/sock.h:607 [inline] > > inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592 > > tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249 > > tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854 > > tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56 > > tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479 > > tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599 > > tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619 > > call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404 > > expire_timers kernel/time/timer.c:1449 [inline] > > __run_timers kernel/time/timer.c:1773 [inline] > > __run_timers kernel/time/timer.c:1740 [inline] > > run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786 > > __do_softirq+0x115/0x33f kernel/softirq.c:292 > > invoke_softirq kernel/softirq.c:373 [inline] > > irq_exit+0xbb/0xe0 kernel/softirq.c:413 > > exiting_irq arch/x86/include/asm/apic.h:536 [inline] > > smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137 > > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830 > > native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71 > > arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571 > > default_idle_call+0x1e/0x40 kernel/sched/idle.c:94 > > cpuidle_idle_call kernel/sched/idle.c:154 [inline] > > do_idle+0x1af/0x280 kernel/sched/idle.c:263 > > cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355 > > rest_init+0xec/0xf6 init/main.c:452 > > arch_call_rest_init+0x17/0x37 > > start_kernel+0x838/0x85e init/main.c:786 > > x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490 > > x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471 > > secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241 > > > > Reported by Kernel Concurrency Sanitizer on: > > CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, > > BIOS Google 01/01/2011 > > Like this? Hmmm... Do you also need this? Thanx, Paul ------------------------------------------------------------------------ commit cf78c8772c9dc26a36c0e5eae1262cc396bbfb3f Author: Paul E. McKenney Date: Sat Nov 9 10:45:47 2019 -0800 rcu: Add a hlist_nulls_unhashed_lockless() function This commit adds an hlist_nulls_unhashed_lockless() to allow lockless checking for whether or note an hlist_nulls_node is hashed or not. While in the area, this commit also adds a docbook comment to the existing hlist_nulls_unhashed() function. Signed-off-by: Paul E. McKenney diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h index 1ecd356..fa6e847 100644 --- a/include/linux/list_nulls.h +++ b/include/linux/list_nulls.h @@ -56,11 +56,33 @@ static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr) return ((unsigned long)ptr) >> 1; } +/** + * hlist_nulls_unhashed - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. + */ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h) { return !h->pprev; } +/** + * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized? + * @h: Node to be checked + * + * Not that not all removal functions will leave a node in unhashed state. + * For example, hlist_del_init_rcu() leaves the node in unhashed state, + * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this + * function may be used locklessly. + */ +static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h) +{ + return !READ_ONCE(h->pprev); +} + static inline int hlist_nulls_empty(const struct hlist_nulls_head *h) { return is_a_nulls(READ_ONCE(h->first));