From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFF063D75DE; Thu, 20 Aug 2026 17:16:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787246211; cv=none; b=CEPovBdOjbG8koAWF4ZY2uyJXMuM7FAbwyGV1LIGHPxawlQKD8CJIvrH55fX0bDGMCsq+GNWYSDW7JQ9jxUw5QDxVouH43CuYyoNogW/6fQaafrolJqInmwAGF+6G6HQ53WcUCTBVjLdRR1hAZDCuyFso4ovZwXzybTr7lgFDOA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787246211; c=relaxed/simple; bh=+1bmV0emnRfGbzkVZrr6Xn06idLHg9fjaOWVq9QhNXQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ogd/B2gR4vdW6ah6SfTkhNRuawNGul2+8LnaqYsboRa10WZE9SU82iBd+L2G2rxMhVNijTswAe0KdGuTtdwqkcAC9zTm9vJftPrWjpgkLEAPdeiBukhmviUK+2fnaBjpA0vVNHljH2Vkui6fiazSzskMRoP+K8jYz6IUVmTTgbQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GwQUAEOK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GwQUAEOK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49B621F000E9; Thu, 20 Aug 2026 17:16:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787246209; bh=MV24uR/6Cop6a5mbcnfeD+N904Fg68fULCFuxI3hmvk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GwQUAEOK7DSZyJoaIvNGzb7eXUjL+lBRclXa6f9EKhUzThVZICr0l1lhMLlnlyDML DGJo2yCn2P0h4yuZXBCTbvh3s0XySxJ7tUIToVru4vMLT+U8yiXNaUVLSKH6kh1twx i4Ui/0D5qTKyEHIV/zWJdMsg1VkSI2JCgOlVxdwdROIV7kipuNr7yESf6rDQb3y5aF xeay2R7Vs0pTkaW9UlzQ+CTuNLuu1o5oxCJTXppmAizyRzgD8vTUbOVdhdmPtG9NLo c7JOdZnGN5lNnVYIVr/lgJbmqVc2OkwC5qEddnCpB365CZgp1Ys95WqI5uYaoY/UCZ vqJymbhwXeWAg== Message-ID: <359ea967-9b97-4584-88e6-bddb4044de2e@kernel.org> Date: Thu, 20 Aug 2026 19:16:05 +0200 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v19 00/40] DEPT(DEPendency Tracker) To: Byungchul Park , linux-kernel@vger.kernel.org Cc: max.byungchul.park@gmail.com, kernel_team@skhynix.com, torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org, joel@joelfernandes.org, sashal@kernel.org, daniel.vetter@ffwll.ch, duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org, tytso@mit.edu, willy@infradead.org, david@fromorbit.com, amir73il@gmail.com, gregkh@linuxfoundation.org, kernel-team@lge.com, linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org, jglisse@redhat.com, dennis@kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, jack@suse.cz, jlayton@kernel.org, dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org, dri-devel@lists.freedesktop.org, rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com, hamohammed.sa@gmail.com, harry.yoo@oracle.com, chris.p.wilson@intel.com, gwan-gyeong.mun@intel.com, boqun.feng@gmail.com, longman@redhat.com, yunseong.kim@ericsson.com, ysk@kzalloc.com, yeoreum.yun@arm.com, netdev@vger.kernel.org, matthew.brost@intel.com, her0gyugyu@gmail.com, corbet@lwn.net, catalin.marinas@arm.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, luto@kernel.org, sumit.semwal@linaro.org, gustavo@padovan.org, christian.koenig@amd.com, andi.shyti@kernel.org, arnd@arndb.de, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, mcgrof@kernel.org, petr.pavlu@suse.com, da.gomez@kernel.org, samitolvanen@google.com, paulmck@kernel.org, frederic@kernel.org, neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com, josh@joshtriplett.org, urezki@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang@linux.dev, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, chuck.lever@oracle.com, neil@brown.name, okorniev@redhat.com, Dai.Ngo@oracle.com, tom@talpey.com, trondmy@kernel.org, anna@kernel.org, kees@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, mark.rutland@arm.com, ada.coupriediaz@arm.com, kristina.martsenko@arm.com, wangkefeng.wang@huawei.com, broonie@kernel.org, kevin.brodsky@arm.com, dwmw@amazon.co.uk, shakeel.butt@linux.dev, ast@kernel.org, ziy@nvidia.com, yuzhao@google.com, baolin.wang@linux.alibaba.com, usamaarif642@gmail.com, joel.granados@kernel.org, richard.weiyang@gmail.com, geert+renesas@glider.be, tim.c.chen@linux.intel.com, linux@treblig.org, alexander.shishkin@linux.intel.com, lillian@star-ark.net, chenhuacai@kernel.org, francesco@valla.it, guoweikang.kernel@gmail.com, link@vivo.com, jpoimboe@kernel.org, masahiroy@kernel.org, brauner@kernel.org, thomas.weissschuh@linutronix.de, oleg@redhat.com, mjguzik@gmail.com, andrii@kernel.org, wangfushuai@baidu.com, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-i2c@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, rcu@vger.kernel.org, linux-nfs@vger.kernel.org, linux-rt-devel@lists.linux.dev, 2407018371@qq.com, dakr@kernel.org, miguel.ojeda.sandonis@gmail.com, neilb@ownmail.net, bagasdotme@gmail.com, wsa+renesas@sang-engineering.com, dave.hansen@intel.com, geert@linux-m68k.org, ojeda@kernel.org, alex.gaynor@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, rust-for-linux@vger.kernel.org References: <20260706061928.66713-1-byungchul@sk.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260706061928.66713-1-byungchul@sk.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/6/26 08:18, Byungchul Park wrote: > Hi Linus and folks, Hi, I think there was plenty of feedback from locking maintainers in the past. One question and a comment below. > > DEPT(DEPendency Tracker) is a runtime deadlock detection framework that > sees what lockdep cannot. > > I'm thrilled to share that DEPT has moved beyond theory and is now > catching real deadlocks in the wild: > > https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SAKURA.ne.jp/ > https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.park@lge.com/ > https://lore.kernel.org/all/b6e00e77-4a8c-4e05-ab79-266bf05fcc2d@igalia.com/ > > I've added comprehensive documentation explaining DEPT's design and usage. > Getting started is as simple as enabling CONFIG_DEPT and watching dmesg. > > THE PROBLEM LOCKDEP CANNOT SOLVE > -------------------------------- > > Lockdep has been our trusted deadlock detector for two decades, but it > has a fundamental blind spot: it tracks lock acquisition order, not the > actual waits and events that cause deadlocks. This means lockdep misses: > > * Deadlocks involving folio locks (not released within the context) > * Cross-context synchronization like wait_for_completion()/complete() > * DMA fence waits, RCU waits, and general waitqueue patterns > * Any synchronization primitive outside the classic lock/unlock model > > Consider this real deadlock pattern that lockdep cannot detect: > > context X context Y context Z > > mutex_lock A > folio_lock B > folio_lock B <- DEADLOCK > mutex_lock A <- DEADLOCK > folio_unlock B > folio_unlock B > mutex_unlock A > mutex_unlock A But that really just boils down to folio lock being implemented as a PG_lock + some advanced wait mechanism. And we must do that because of lack of bits in struct page. Willy mentioned in a previous version [1]: "I don't think it makes sense to track lock state in the page (nor folio). Partly because there's just so many of them, but also because the locking rules don't really apply to individual folios so much as they do to the mappings (or anon_vmas) that contain folios." Given that lockdep is a debug feature, and we will at some point allocate struct folio separately, I assume we could just squeeze a "struct lockdep_map" in there in such debug configs and the world would not collapse. Doing that today (one "struct lockdep_map" in each "struct page") wouldn't work as mm_zero_struct_page() would not expect such large "struct page". But conceptually, for a debug kernel with a special CONFIG_LOCKDEP_PAGE_LOCK, maybe that would already be ok and we could just do that (and optimize it as we allocate folios separately). Not that it's ideal, but for a debug feature to at least check PG_lock, probably an easier way to achieve it than some completely new infrastructure. Now, Willy said "locking rules don't really apply to individual folios", I wonder if that could just help to also let lockdep check PG_lock with less metadata? (didn't fully wrap my head around the implications) [1] https://lore.kernel.org/all/aR3WHf9QZ_dizNun@casper.infradead.org/?utm_source=chatgpt.com It's your guiding example, that's why I mention it. You do mention other wait cases here, I don't know anything about them, but for folios it's really just "we used a single bit so far" AFAIKs. [...] > > Q. Why not build DEPT into lockdep? > > A. Lockdep is stable, battle-tested code. I chose separation because > while DEPT borrows BFS and hashing ideas, the wait/event model > requires rebuilding from scratch. Lockdep was designed for lock > acquisition order — retrofitting it would risk its stability. Why can't this just be some configurable extension to lockdep (CONFIG_LOCKDEP_XYZ) until the feature is stable and can unconditionally be enabled along with it? I don't quite buy the "would risk its stability" argument. A lot of stuff we do "risks stability", every day :) Is there another good reason (incompatible with X, dangerous with Y, cinfusing Z) why this really must be a separate thing? > > Q. Will DEPT replace lockdep? > > A. No. Lockdep validates correct lock usage — that's not going away. > DEPT supersedes only the dependency-checking logic when mature. It's quite unfortunate that we'd end up with another similar-but-different mechanism, that will just end up confusing people. But I am not a locking maintainer. I think there was plenty of discussion in the past, so I might just be raising points that were already discussed in the past, but I really just read some random pieces of earlier discussions. (ideally previous discussions would be summarized here) Long story short: we are now in v19 and I think there was pushback in the past. Did the opinion of locking maintainers change, or is there a way forward to integrate this in a way that would make locking maintainers accept this? -- Cheers, David