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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 B25B9C4CECE for ; Fri, 13 Mar 2020 09:33:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 780E82073E for ; Fri, 13 Mar 2020 09:33:32 +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="sh9MXIhM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726512AbgCMJdb (ORCPT ); Fri, 13 Mar 2020 05:33:31 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:35922 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726364AbgCMJda (ORCPT ); Fri, 13 Mar 2020 05:33:30 -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=8pIGnk90C/eQbLnJ8p/15sfKmAvXSjOcwPwug3juja8=; b=sh9MXIhMbMo/jyATdPSOXudhHQ RAfYggc+QFxGmSCG2DbiXet21j7htLbmuakEwuPEsVTrSWNMYhaGSrcoj5Gh8nUzspgVTa98SicQE XrAh1FHucHldANEXZEBGVBcjaZ4V0k0BxPhJIrxY/LEzXu2QtCdS9ubYgedFZZPkAvfvazWmagsZD o4yMRmLzCdzVEvMW+yA08A+Ax85RnlHOEdwKaocMuWVvTWZ3s53c1CtKfxMwEo9bCqAOcCHnpQ3Vj jKU/B0Yj1ZS2obQDcjp4cTEqsZwhq4hAVyfNLzZPbG6DkhpbVf/jKE+Sn5JLB4N+VVosLcINBIkMZ 7bbuTV0Q==; 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 1jCgh6-0005WP-67; Fri, 13 Mar 2020 09:33:28 +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 D01153011E0; Fri, 13 Mar 2020 10:33:25 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9759A214344F4; Fri, 13 Mar 2020 10:33:25 +0100 (CET) Date: Fri, 13 Mar 2020 10:33:25 +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: <20200313093325.GW12561@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: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 12, 2020 at 11:12:55PM +0800, Boqun Feng wrote: Thanks! > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 32406ef0d6a2..5142a6b11bf5 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1719,9 +1719,11 @@ unsigned long lockdep_count_forward_deps(struct lock_class *class) > this.class = class; > > raw_local_irq_save(flags); > + current->lockdep_recursion = 1; > arch_spin_lock(&lockdep_lock); > ret = __lockdep_count_forward_deps(&this); > arch_spin_unlock(&lockdep_lock); > + current->lockdep_recursion = 0; > raw_local_irq_restore(flags); > > return ret; > @@ -1746,9 +1748,11 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class) > this.class = class; > > raw_local_irq_save(flags); > + current->lockdep_recursion = 1; > arch_spin_lock(&lockdep_lock); > ret = __lockdep_count_backward_deps(&this); > arch_spin_unlock(&lockdep_lock); > + current->lockdep_recursion = 0; > raw_local_irq_restore(flags); > > return ret; This copies a bad pattern though; all the sites that do not check lockdep_recursion_count first really should be using ++/-- instead. But I just found there are indeed already a few sites that violate this. I've taken this patch and done a general fixup on top. --- Subject: locking/lockdep: Fix bad recursion pattern From: Peter Zijlstra Date: Fri Mar 13 09:56:38 CET 2020 There were two patterns for lockdep_recursion: Pattern-A: if (current->lockdep_recursion) return current->lockdep_recursion = 1; /* do stuff */ current->lockdep_recursion = 0; Pattern-B: current->lockdep_recursion++; /* do stuff */ current->lockdep_recursion--; But a third pattern has emerged: Pattern-C: current->lockdep_recursion = 1; /* do stuff */ current->lockdep_recursion = 0; And while this isn't broken per-se, it is highly dangerous because it doesn't nest properly. Get rid of all Pattern-C instances and shore up Pattern-A with a warning. Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/lockdep.c | 74 +++++++++++++++++++++++++---------------------- 1 file changed, 40 insertions(+), 34 deletions(-) --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -389,6 +389,12 @@ void lockdep_on(void) } EXPORT_SYMBOL(lockdep_on); +static inline void lockdep_recursion_finish(void) +{ + if (WARN_ON_ONCE(--current->lockdep_recursion)) + current->lockdep_recursion = 0; +} + void lockdep_set_selftest_task(struct task_struct *task) { lockdep_selftest_task_struct = task; @@ -1719,11 +1725,11 @@ unsigned long lockdep_count_forward_deps this.class = class; raw_local_irq_save(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; arch_spin_lock(&lockdep_lock); ret = __lockdep_count_forward_deps(&this); arch_spin_unlock(&lockdep_lock); - current->lockdep_recursion = 0; + current->lockdep_recursion--; raw_local_irq_restore(flags); return ret; @@ -1748,11 +1754,11 @@ unsigned long lockdep_count_backward_dep this.class = class; raw_local_irq_save(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; arch_spin_lock(&lockdep_lock); ret = __lockdep_count_backward_deps(&this); arch_spin_unlock(&lockdep_lock); - current->lockdep_recursion = 0; + current->lockdep_recursion--; raw_local_irq_restore(flags); return ret; @@ -3433,9 +3439,9 @@ void lockdep_hardirqs_on(unsigned long i if (DEBUG_LOCKS_WARN_ON(current->hardirq_context)) return; - current->lockdep_recursion = 1; + current->lockdep_recursion++; __trace_hardirqs_on_caller(ip); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); } NOKPROBE_SYMBOL(lockdep_hardirqs_on); @@ -3491,7 +3497,7 @@ void trace_softirqs_on(unsigned long ip) return; } - current->lockdep_recursion = 1; + current->lockdep_recursion++; /* * We'll do an OFF -> ON transition: */ @@ -3506,7 +3512,7 @@ void trace_softirqs_on(unsigned long ip) */ if (curr->hardirqs_enabled) mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); } /* @@ -3759,9 +3765,9 @@ void lockdep_init_map(struct lockdep_map return; raw_local_irq_save(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; register_lock_class(lock, subclass, 1); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } } @@ -4441,11 +4447,11 @@ void lock_set_class(struct lockdep_map * return; raw_local_irq_save(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; check_flags(flags); if (__lock_set_class(lock, name, key, subclass, ip)) check_chain_key(current); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_set_class); @@ -4458,11 +4464,11 @@ void lock_downgrade(struct lockdep_map * return; raw_local_irq_save(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; check_flags(flags); if (__lock_downgrade(lock, ip)) check_chain_key(current); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_downgrade); @@ -4483,11 +4489,11 @@ void lock_acquire(struct lockdep_map *lo raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip); __lock_acquire(lock, subclass, trylock, read, check, irqs_disabled_flags(flags), nest_lock, ip, 0, 0); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_acquire); @@ -4501,11 +4507,11 @@ void lock_release(struct lockdep_map *lo raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; trace_lock_release(lock, ip); if (__lock_release(lock, ip)) check_chain_key(current); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_release); @@ -4521,9 +4527,9 @@ int lock_is_held_type(const struct lockd raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; ret = __lock_is_held(lock, read); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); return ret; @@ -4542,9 +4548,9 @@ struct pin_cookie lock_pin_lock(struct l raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; cookie = __lock_pin_lock(lock); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); return cookie; @@ -4561,9 +4567,9 @@ void lock_repin_lock(struct lockdep_map raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; __lock_repin_lock(lock, cookie); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_repin_lock); @@ -4578,9 +4584,9 @@ void lock_unpin_lock(struct lockdep_map raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; __lock_unpin_lock(lock, cookie); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_unpin_lock); @@ -4716,10 +4722,10 @@ void lock_contended(struct lockdep_map * raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; trace_lock_contended(lock, ip); __lock_contended(lock, ip); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_contended); @@ -4736,9 +4742,9 @@ void lock_acquired(struct lockdep_map *l raw_local_irq_save(flags); check_flags(flags); - current->lockdep_recursion = 1; + current->lockdep_recursion++; __lock_acquired(lock, ip); - current->lockdep_recursion = 0; + lockdep_recursion_finish(); raw_local_irq_restore(flags); } EXPORT_SYMBOL_GPL(lock_acquired); @@ -4963,7 +4969,7 @@ static void free_zapped_rcu(struct rcu_h raw_local_irq_save(flags); arch_spin_lock(&lockdep_lock); - current->lockdep_recursion = 1; + current->lockdep_recursion++; /* closed head */ pf = delayed_free.pf + (delayed_free.index ^ 1); @@ -4975,7 +4981,7 @@ static void free_zapped_rcu(struct rcu_h */ call_rcu_zapped(delayed_free.pf + delayed_free.index); - current->lockdep_recursion = 0; + current->lockdep_recursion--; arch_spin_unlock(&lockdep_lock); raw_local_irq_restore(flags); } @@ -5022,11 +5028,11 @@ static void lockdep_free_key_range_reg(v raw_local_irq_save(flags); arch_spin_lock(&lockdep_lock); - current->lockdep_recursion = 1; + current->lockdep_recursion++; pf = get_pending_free(); __lockdep_free_key_range(pf, start, size); call_rcu_zapped(pf); - current->lockdep_recursion = 0; + current->lockdep_recursion--; arch_spin_unlock(&lockdep_lock); raw_local_irq_restore(flags);