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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 753B8C4CECE for ; Fri, 13 Mar 2020 10:21:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6A4D42073E for ; Fri, 13 Mar 2020 10:21:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jmgce857" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726414AbgCMKVM (ORCPT ); Fri, 13 Mar 2020 06:21:12 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:59200 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726364AbgCMKVM (ORCPT ); Fri, 13 Mar 2020 06:21:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=UNS9qfdE8QK8g+6d8TkL9IzCb5kYV8ynuRbXqP8orQU=; b=jmgce857R/Quhq12vgQJA2bK3P dNHeyC0SfGhC4DosYbWBYqqNOswRjd0HLKNNT4sD1H+aTUZX8ohBg15HghZ0LQ7R5/gYAKbd4+XZ2 KMpf2a+NoSgJiDnYTvrFPX8ZeMyfKT4u8rK0FqN2VWlCUrWZQgjd9Vq5LF27KP3iZT/cC1PA8nd/i vbc3PwQULoSQlRwoNHbknjO3WsZlfNOGpUf2QRdc+2RmqvPp2wZm5Ebsh2L+4k3mVqzZPxkWOr539 no9JCHgd6mUS6yxMxoMXDu+jWCFNAI+PIrslYQq+n1fR6WCEdrThvSHTj/pFXNdGdmZnWNjb/iD/8 LqolF4sw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jChRF-00077H-SL; Fri, 13 Mar 2020 10:21:10 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 11629300470; Fri, 13 Mar 2020 11:21:08 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id F3A822B64FF63; Fri, 13 Mar 2020 11:21:07 +0100 (CET) Date: Fri, 13 Mar 2020 11:21:07 +0100 From: Peter Zijlstra To: Boqun Feng Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, "Joel Fernandes (Google)" , "Paul E. McKenney" , Madhuparna Bhowmik , Qian Cai , Ingo Molnar , Will Deacon Subject: Re: [PATCH] locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward_deps() Message-ID: <20200313102107.GX12561@hirez.programming.kicks-ass.net> References: <20200312151258.128036-1-boqun.feng@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312151258.128036-1-boqun.feng@gmail.com> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Mar 12, 2020 at 11:12:55PM +0800, Boqun Feng wrote: > The warning got triggered because lockdep_count_forward_deps() call > __bfs() without current->lockdep_recursion being set, as a result > a lockdep internal function (__bfs()) is checked by lockdep, which is > unexpected, and the inconsistency between the irq-off state and the > state traced by lockdep caused the warning. This also had me look at __bfs(), while there is a WARN in there, it doesn't really assert all the expectations. This lead to the below patch. --- Subject: locking/lockdep: Rework lockdep_lock From: Peter Zijlstra Date: Fri Mar 13 11:09:49 CET 2020 A few sites want to assert we own the graph_lock/lockdep_lock, provide a more conventional lock interface for it with a number of trivial debug checks. Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/lockdep.c | 89 +++++++++++++++++++++++++---------------------- 1 file changed, 48 insertions(+), 41 deletions(-) --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -84,12 +84,39 @@ module_param(lock_stat, int, 0644); * to use a raw spinlock - we really dont want the spinlock * code to recurse back into the lockdep code... */ -static arch_spinlock_t lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; +static arch_spinlock_t __lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; +static struct task_struct *__owner; + +static inline void lockdep_lock(void) +{ + DEBUG_LOCKS_WARN_ON(!irqs_disabled()); + + arch_spin_lock(&__lock); + __owner = current; + current->lockdep_recursion++; +} + +static inline void lockdep_unlock(void) +{ + if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current)) + return; + + current->lockdep_recursion--; + __owner = NULL; + arch_spin_unlock(&__lock); +} + +static inline bool lockdep_assert_locked(void) +{ + return DEBUG_LOCKS_WARN_ON(__owner != current); +} + static struct task_struct *lockdep_selftest_task_struct; + static int graph_lock(void) { - arch_spin_lock(&lockdep_lock); + lockdep_lock(); /* * Make sure that if another CPU detected a bug while * walking the graph we dont change it (while the other @@ -97,27 +124,15 @@ static int graph_lock(void) * dropped already) */ if (!debug_locks) { - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); return 0; } - /* prevent any recursions within lockdep from causing deadlocks */ - current->lockdep_recursion++; return 1; } -static inline int graph_unlock(void) +static inline void graph_unlock(void) { - if (debug_locks && !arch_spin_is_locked(&lockdep_lock)) { - /* - * The lockdep graph lock isn't locked while we expect it to - * be, we're confused now, bye! - */ - return DEBUG_LOCKS_WARN_ON(1); - } - - current->lockdep_recursion--; - arch_spin_unlock(&lockdep_lock); - return 0; + lockdep_unlock(); } /* @@ -128,7 +143,7 @@ static inline int debug_locks_off_graph_ { int ret = debug_locks_off(); - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); return ret; } @@ -1475,6 +1490,8 @@ static int __bfs(struct lock_list *sourc struct circular_queue *cq = &lock_cq; int ret = 1; + lockdep_assert_locked(); + if (match(source_entry, data)) { *target_entry = source_entry; ret = 0; @@ -1497,8 +1514,6 @@ static int __bfs(struct lock_list *sourc head = get_dep_list(lock, offset); - DEBUG_LOCKS_WARN_ON(!irqs_disabled()); - list_for_each_entry_rcu(entry, head, entry) { if (!lock_accessed(entry)) { unsigned int cq_depth; @@ -1725,11 +1740,9 @@ unsigned long lockdep_count_forward_deps this.class = class; raw_local_irq_save(flags); - current->lockdep_recursion++; - arch_spin_lock(&lockdep_lock); + lockdep_lock(); ret = __lockdep_count_forward_deps(&this); - arch_spin_unlock(&lockdep_lock); - current->lockdep_recursion--; + lockdep_unlock(); raw_local_irq_restore(flags); return ret; @@ -1754,11 +1767,9 @@ unsigned long lockdep_count_backward_dep this.class = class; raw_local_irq_save(flags); - current->lockdep_recursion++; - arch_spin_lock(&lockdep_lock); + lockdep_lock(); ret = __lockdep_count_backward_deps(&this); - arch_spin_unlock(&lockdep_lock); - current->lockdep_recursion--; + lockdep_unlock(); raw_local_irq_restore(flags); return ret; @@ -2813,7 +2824,7 @@ static inline int add_chain_cache(struct * disabled to make this an IRQ-safe lock.. for recursion reasons * lockdep won't complain about its own locking errors. */ - if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) + if (lockdep_assert_locked()) return 0; chain = alloc_lock_chain(); @@ -4968,8 +4979,7 @@ static void free_zapped_rcu(struct rcu_h return; raw_local_irq_save(flags); - arch_spin_lock(&lockdep_lock); - current->lockdep_recursion++; + lockdep_lock(); /* closed head */ pf = delayed_free.pf + (delayed_free.index ^ 1); @@ -4981,8 +4991,7 @@ static void free_zapped_rcu(struct rcu_h */ call_rcu_zapped(delayed_free.pf + delayed_free.index); - current->lockdep_recursion--; - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); raw_local_irq_restore(flags); } @@ -5027,13 +5036,11 @@ static void lockdep_free_key_range_reg(v init_data_structures_once(); raw_local_irq_save(flags); - arch_spin_lock(&lockdep_lock); - current->lockdep_recursion++; + lockdep_lock(); pf = get_pending_free(); __lockdep_free_key_range(pf, start, size); call_rcu_zapped(pf); - current->lockdep_recursion--; - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); raw_local_irq_restore(flags); /* @@ -5055,10 +5062,10 @@ static void lockdep_free_key_range_imm(v init_data_structures_once(); raw_local_irq_save(flags); - arch_spin_lock(&lockdep_lock); + lockdep_lock(); __lockdep_free_key_range(pf, start, size); __free_zapped_classes(pf); - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); raw_local_irq_restore(flags); } @@ -5154,10 +5161,10 @@ static void lockdep_reset_lock_imm(struc unsigned long flags; raw_local_irq_save(flags); - arch_spin_lock(&lockdep_lock); + lockdep_lock(); __lockdep_reset_lock(pf, lock); __free_zapped_classes(pf); - arch_spin_unlock(&lockdep_lock); + lockdep_unlock(); raw_local_irq_restore(flags); }