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 60C33C46467 for ; Thu, 19 Jan 2023 13:34:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231315AbjASNec (ORCPT ); Thu, 19 Jan 2023 08:34:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231265AbjASNeP (ORCPT ); Thu, 19 Jan 2023 08:34:15 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 617B87CCC7; Thu, 19 Jan 2023 05:34:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=Dd4KE++vWIKamqThkehHj7fJpHW3aChCNzZyFef73OI=; b=ZiBP9IU8e0RQ32NiZKka8MnWTR Dn0s9lTcFdzt4feEZuNn6vIgEPzmD5cviY4HNiw+EGim/+fdqSp83CwedDaJFyd2q2vePAOMF7R47 /mT/pV3FrXZ0OCNIOm/rgdNiJAiF9udqbmgCvdv8tlfjrQES8QDp+06hIwoNapYXBTR+i6XKWX5ij qkK3CEH0iS8hZp+JgId9L10gYqA1yZnepzrHrEzU/DThBM4jGZH4pD6906x9w3V5a2ZVJlG7+GsLd IX8t76QoYPJmUT+lx0lOj7EEt0PIr724UtBaPXC85udHqrL+r1umcOCxsWYgULtsg+F/hymdVlFkZ MS0yEAZA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pIV3G-00106x-OP; Thu, 19 Jan 2023 13:33:58 +0000 Date: Thu, 19 Jan 2023 13:33:58 +0000 From: Matthew Wilcox To: Byungchul Park Cc: boqun.feng@gmail.com, linux-kernel@vger.kernel.org, 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, 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, paolo.valente@linaro.org, josef@toxicpanda.com, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, 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, 42.hyeyoo@gmail.com, chris.p.wilson@intel.com, gwan-gyeong.mun@intel.com, max.byungchul.park@gmail.com, longman@redhat.com Subject: Re: [PATCH RFC v7 00/23] DEPT(Dependency Tracker) Message-ID: References: <1674109388-6663-1-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1674109388-6663-1-git-send-email-byungchul.park@lge.com> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Thu, Jan 19, 2023 at 03:23:08PM +0900, Byungchul Park wrote: > Boqun wrote: > > * Looks like the DEPT dependency graph doesn't handle the > > fair/unfair readers as lockdep current does. Which bring the > > next question. > > No. DEPT works better for unfair read. It works based on wait/event. So > read_lock() is considered a potential wait waiting on write_unlock() > while write_lock() is considered a potential wait waiting on either > write_unlock() or read_unlock(). DEPT is working perfect for it. > > For fair read (maybe you meant queued read lock), I think the case > should be handled in the same way as normal lock. I might get it wrong. > Please let me know if I miss something. >From the lockdep/DEPT point of view, the question is whether: read_lock(A) read_lock(A) can deadlock if a writer comes in between the two acquisitions and sleeps waiting on A to be released. A fair lock will block new readers when a writer is waiting, while an unfair lock will allow new readers even while a writer is waiting.