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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> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 7947B4001B X-Stat-Signature: 319dg68kqa9d8bqp8eopcq97zkunojkt X-Rspam-User: X-HE-Tag: 1674135281-44050 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.