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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0B58C67871 for ; Mon, 16 Jan 2023 22:22:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234018AbjAPWWB (ORCPT ); Mon, 16 Jan 2023 17:22:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55064 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230420AbjAPWV4 (ORCPT ); Mon, 16 Jan 2023 17:21:56 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47E371CAC8 for ; Mon, 16 Jan 2023 14:21:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673907672; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kdJEu7MIJ0YE7tvR/uF5pyHEa3dRvgT+GaMoWFZbJiw=; b=RCzAOGfN0zCk49vg4pqDd1n3yjwg+TIrGwgzJ1FT83yr+iUlRg1hVK2KXcWfazNjmnyGI4 7Y2JRIB/KyY6Dft7E7rdEhQDrqbUNJqCHer9Gqh1e3E4KKAAkVyxRe3BkjqLMTNfU54htS OwZg4XVJ0ES4pBTCz+BdkrQf715sv18= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-352-qbuL4ohUPBylS5bkdRswgQ-1; Mon, 16 Jan 2023 17:21:10 -0500 X-MC-Unique: qbuL4ohUPBylS5bkdRswgQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id EB64E85CBE7; Mon, 16 Jan 2023 22:21:09 +0000 (UTC) Received: from [10.22.18.0] (unknown [10.22.18.0]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3F004492B00; Mon, 16 Jan 2023 22:21:09 +0000 (UTC) Message-ID: <221e35b8-88f5-5fc5-6961-6a8ce060a97b@redhat.com> Date: Mon, 16 Jan 2023 17:21:09 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH 4/3] locking/lockdep: Improve the deadlock scenario print for sync and read lock Content-Language: en-US To: Boqun Feng , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, kvm@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Lai Jiangshan , "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , David Woodhouse , Paolo Bonzini , seanjc@google.com, Joel Fernandes , Matthew Wilcox , Michal Luczaj References: <20230113065955.815667-1-boqun.feng@gmail.com> <20230113235722.1226525-1-boqun.feng@gmail.com> From: Waiman Long In-Reply-To: <20230113235722.1226525-1-boqun.feng@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/13/23 18:57, Boqun Feng wrote: > Lock scenario print is always a weak spot of lockdep splats. Improvement > can be made if we rework the dependency search and the error printing. > > However without touching the graph search, we can improve a little for > the circular deadlock case, since we have the to-be-added lock > dependency, and know whether these two locks are read/write/sync. > > In order to know whether a held_lock is sync or not, a bit was > "stolen" from ->references, which reduce our limit for the same lock > class nesting from 2^12 to 2^11, and it should still be good enough. > > Besides, since we now have bit in held_lock for sync, we don't need the > "hardirqoffs being 1" trick, and also we can avoid the __lock_release() > if we jump out of __lock_acquire() before the held_lock stored. > > With these changes, a deadlock case evolved with read lock and sync gets > a better print-out from: > > [...] Possible unsafe locking scenario: > [...] > [...] CPU0 CPU1 > [...] ---- ---- > [...] lock(srcuA); > [...] lock(srcuB); > [...] lock(srcuA); > [...] lock(srcuB); > > to > > [...] Possible unsafe locking scenario: > [...] > [...] CPU0 CPU1 > [...] ---- ---- > [...] rlock(srcuA); > [...] lock(srcuB); > [...] lock(srcuA); > [...] sync(srcuB); > > Signed-off-by: Boqun Feng > --- > include/linux/lockdep.h | 3 ++- > kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++-------------- > 2 files changed, 34 insertions(+), 17 deletions(-) > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h > index ba09df6a0872..febd7ecc225c 100644 > --- a/include/linux/lockdep.h > +++ b/include/linux/lockdep.h > @@ -134,7 +134,8 @@ struct held_lock { > unsigned int read:2; /* see lock_acquire() comment */ > unsigned int check:1; /* see lock_acquire() comment */ > unsigned int hardirqs_off:1; > - unsigned int references:12; /* 32 bits */ > + unsigned int sync:1; > + unsigned int references:11; /* 32 bits */ > unsigned int pin_count; > }; > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index cffa026a765f..4031d87f6829 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1880,6 +1880,8 @@ print_circular_lock_scenario(struct held_lock *src, > struct lock_class *source = hlock_class(src); > struct lock_class *target = hlock_class(tgt); > struct lock_class *parent = prt->class; > + int src_read = src->read; > + int tgt_read = tgt->read; > > /* > * A direct locking problem where unsafe_class lock is taken > @@ -1907,7 +1909,10 @@ print_circular_lock_scenario(struct held_lock *src, > printk(" Possible unsafe locking scenario:\n\n"); > printk(" CPU0 CPU1\n"); > printk(" ---- ----\n"); > - printk(" lock("); > + if (tgt_read != 0) > + printk(" rlock("); > + else > + printk(" lock("); > __print_lock_name(target); > printk(KERN_CONT ");\n"); > printk(" lock("); > @@ -1916,7 +1921,12 @@ print_circular_lock_scenario(struct held_lock *src, > printk(" lock("); > __print_lock_name(target); > printk(KERN_CONT ");\n"); > - printk(" lock("); > + if (src_read != 0) > + printk(" rlock("); > + else if (src->sync) > + printk(" sync("); > + else > + printk(" lock("); > __print_lock_name(source); > printk(KERN_CONT ");\n"); > printk("\n *** DEADLOCK ***\n\n"); src can be sync() but not the target. Is there a reason why that is the case? > @@ -4530,7 +4540,13 @@ mark_usage(struct task_struct *curr, struct held_lock *hlock, int check) > return 0; > } > } > - if (!hlock->hardirqs_off) { > + > + /* > + * For lock_sync(), don't mark the ENABLED usage, since lock_sync() > + * creates no critical section and no extra dependency can be introduced > + * by interrupts > + */ > + if (!hlock->hardirqs_off && !hlock->sync) { > if (hlock->read) { > if (!mark_lock(curr, hlock, > LOCK_ENABLED_HARDIRQ_READ)) > @@ -4909,7 +4925,7 @@ static int __lock_is_held(const struct lockdep_map *lock, int read); > static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > int trylock, int read, int check, int hardirqs_off, > struct lockdep_map *nest_lock, unsigned long ip, > - int references, int pin_count) > + int references, int pin_count, int sync) > { > struct task_struct *curr = current; > struct lock_class *class = NULL; > @@ -4960,7 +4976,8 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > > class_idx = class - lock_classes; > > - if (depth) { /* we're holding locks */ > + if (depth && !sync) { > + /* we're holding locks and the new held lock is not a sync */ > hlock = curr->held_locks + depth - 1; > if (hlock->class_idx == class_idx && nest_lock) { > if (!references) > @@ -4994,6 +5011,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > hlock->trylock = trylock; > hlock->read = read; > hlock->check = check; > + hlock->sync = !!sync; > hlock->hardirqs_off = !!hardirqs_off; > hlock->references = references; > #ifdef CONFIG_LOCK_STAT > @@ -5055,6 +5073,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, > if (!validate_chain(curr, hlock, chain_head, chain_key)) > return 0; > > + /* For lock_sync(), we are done here since no actual critical section */ > + if (hlock->sync) > + return 1; > + > curr->curr_chain_key = chain_key; > curr->lockdep_depth++; > check_chain_key(curr); Even with sync, there is still a corresponding lock_acquire() and lock_release(), you can't exit here without increasing lockdep_depth. That can cause underflow. Cheers, Longman