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Date: Mon, 9 May 2022 10:22:02 +0900 From: Byungchul Park <byungchul.park@....com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Damien Le Moal <damien.lemoal@...nsource.wdc.com>, linux-ide@...r.kernel.org, Andreas Dilger <adilger.kernel@...ger.ca>, Ext4 Developers List <linux-ext4@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Joel Fernandes <joel@...lfernandes.org>, Sasha Levin <sashal@...nel.org>, Daniel Vetter <daniel.vetter@...ll.ch>, Chris Wilson <chris@...is-wilson.co.uk>, duyuyang@...il.com, johannes.berg@...el.com, Tejun Heo <tj@...nel.org>, Theodore Ts'o <tytso@....edu>, Matthew Wilcox <willy@...radead.org>, Dave Chinner <david@...morbit.com>, Amir Goldstein <amir73il@...il.com>, "J. Bruce Fields" <bfields@...ldses.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, kernel-team@....com, Linux-MM <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...nel.org>, Minchan Kim <minchan@...nel.org>, Johannes Weiner <hannes@...xchg.org>, Vladimir Davydov <vdavydov.dev@...il.com>, sj@...nel.org, Jerome Glisse <jglisse@...hat.com>, Dennis Zhou <dennis@...nel.org>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, ngupta@...are.org, linux-block <linux-block@...r.kernel.org>, paolo.valente@...aro.org, Josef Bacik <josef@...icpanda.com>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, jack@...e.com, Jeff Layton <jlayton@...nel.org>, Dan Williams <dan.j.williams@...el.com>, Christoph Hellwig <hch@...radead.org>, "Darrick J. Wong" <djwong@...nel.org>, dri-devel <dri-devel@...ts.freedesktop.org>, Dave Airlie <airlied@...ux.ie>, rodrigosiqueiramelo@...il.com, melissa.srw@...il.com, hamohammed.sa@...il.com, 42.hyeyoo@...il.com Subject: Re: [PATCH RFC v6 00/21] DEPT(Dependency Tracker) On Wed, May 04, 2022 at 11:17:02AM -0700, Linus Torvalds wrote: > On Wed, May 4, 2022 at 1:19 AM Byungchul Park <byungchul.park@....com> wrote: > > > > Hi Linus and folks, > > > > I've been developing a tool for detecting deadlock possibilities by > > tracking wait/event rather than lock(?) acquisition order to try to > > cover all synchonization machanisms. > > So what is the actual status of reports these days? I'd like to mention one important thing here. Reportability would get stronger if the more wait-event pairs get tagged everywhere DEPT can work. Everything e.g. HW-SW interface, any retry logic and so on can be a wait-event pair if they work wait or event anyway. For example, polling on an IO mapped read register and initiating the HW to go for the event also can be a pair. Definitely those make DEPT more useful. --- The way to use the APIs: 1. Define SDT(Simple Dependency Tracker) DEFINE_DEPT_SDT(my_hw_event); <- add this 2. Tag on the waits sdt_wait(&my_hw_event); <- add this ... retry logic until my hw work done ... <- the original code 3. Tag on the events sdt_event(&my_hw_event); <- add this run_my_hw(); <- the original code --- These are all we should do. I believe DEPT would be a very useful tool once all wait-event pairs get tagged by the developers in all subsystems and device drivers. Byungchul > Last time I looked at some reports, it gave a lot of false positives > due to mis-understanding prepare_to_sleep(). > > For this all to make sense, it would need to not have false positives > (or at least a very small number of them together with a way to sanely > get rid of them), and also have a track record of finding things that > lockdep doesn't. > > Maybe such reports have been sent out with the current situation, and > I haven't seen them. > > Linus
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