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Date: Sat, 7 May 2022 16:20:50 +0900 From: Hyeonggon Yoo <42.hyeyoo@...il.com> To: Byungchul Park <byungchul.park@....com> Cc: torvalds@...ux-foundation.org, damien.lemoal@...nsource.wdc.com, linux-ide@...r.kernel.org, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, mingo@...hat.com, linux-kernel@...r.kernel.org, peterz@...radead.org, will@...nel.org, tglx@...utronix.de, rostedt@...dmis.org, joel@...lfernandes.org, sashal@...nel.org, daniel.vetter@...ll.ch, chris@...is-wilson.co.uk, duyuyang@...il.com, johannes.berg@...el.com, tj@...nel.org, tytso@....edu, willy@...radead.org, david@...morbit.com, amir73il@...il.com, gregkh@...uxfoundation.org, kernel-team@....com, linux-mm@...ck.org, akpm@...ux-foundation.org, mhocko@...nel.org, minchan@...nel.org, hannes@...xchg.org, vdavydov.dev@...il.com, sj@...nel.org, jglisse@...hat.com, dennis@...nel.org, cl@...ux.com, penberg@...nel.org, rientjes@...gle.com, vbabka@...e.cz, ngupta@...are.org, linux-block@...r.kernel.org, paolo.valente@...aro.org, josef@...icpanda.com, linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk, jack@...e.cz, jack@...e.com, jlayton@...nel.org, dan.j.williams@...el.com, hch@...radead.org, djwong@...nel.org, dri-devel@...ts.freedesktop.org, airlied@...ux.ie, rodrigosiqueiramelo@...il.com, melissa.srw@...il.com, hamohammed.sa@...il.com Subject: Re: [PATCH RFC v6 00/21] DEPT(Dependency Tracker) On Fri, May 06, 2022 at 09:11:35AM +0900, Byungchul Park wrote: > Linus 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? > > > > Last time I looked at some reports, it gave a lot of false positives > > due to mis-understanding prepare_to_sleep(). > > Yes, it was. I handled the case in the following way: > > 1. Stage the wait at prepare_to_sleep(), which might be used at commit. > Which has yet to be an actual wait that Dept considers. > 2. If the condition for sleep is true, the wait will be committed at > __schedule(). The wait becomes an actual one that Dept considers. > 3. If the condition is false and the task gets back to TASK_RUNNING, > clean(=reset) the staged wait. > > That way, Dept only works with what actually hits to __schedule() for > the waits through 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 > > Yes. I agree with you. I got rid of them that way I described above. > IMHO DEPT should not report what lockdep allows (Not talking about wait events). I mean lockdep allows some kind of nested locks but DEPT reports them. When I was collecting reports from DEPT on varous configurations, Most of them was report of down_write_nested(), which is allowed in lockdep. DEPT should not report at least what we know it's not a real deadlock. Otherwise there will be reports that is never fixed, which is quite unpleasant and reporters cannot examine all of them if it's real deadlock or not. > > get rid of them), and also have a track record of finding things that > > lockdep doesn't. > > I have some reports that wait_for_completion or waitqueue is involved. > It's worth noting those are not tracked by Lockdep. I'm checking if > those are true positive or not. I will share those reports once I get > more convinced for that. > > > Maybe such reports have been sent out with the current situation, and > > I haven't seen them. > > Dept reports usually have been sent to me privately, not in LKML. As I > told you, I'm planning to share them. > > Byungchul > > > > > Linus > > -- Thanks, Hyeonggon
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