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Date: Tue, 10 May 2022 08:38:38 +0900 From: Byungchul Park <byungchul.park@....com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>, 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, 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 Mon, May 09, 2022 at 04:47:12PM -0400, Steven Rostedt wrote: > On Mon, 9 May 2022 09:16:37 +0900 > Byungchul Park <byungchul.park@....com> wrote: > > > CASE 2. > > > > lock L with depth n > > lock A > > lock_nested L' with depth n + 1 > > ... > > unlock L' > > unlock A > > unlock L > > > > This case is allowed by Lockdep. > > This case is *NOT* allowed by DEPT cuz it's a *DEADLOCK*. > > > > --- > > > > The following scenario would explain why CASE 2 is problematic. > > > > THREAD X THREAD Y > > > > lock L with depth n > > lock L' with depth n > > lock A > > lock A > > lock_nested L' with depth n + 1 > > I'm confused by what exactly you are saying is a deadlock above. > > Are you saying that lock A and L' are inversed? If so, lockdep had better Hi Steven, Yes, I was talking about A and L'. > detect that regardless of L. A nested lock associates the the nesting with When I checked Lockdep code, L' with depth n + 1 and L' with depth n have different classes in Lockdep. That's why I said Lockdep cannot detect it. By any chance, has it changed so as to consider this case? Or am I missing something? > the same type of lock. That is, in lockdep nested tells lockdep not to > trigger on the L and L' but it will not ignore that A was taken. It will not ignore A but it would work like this: THREAD X THREAD Y lock Ln lock Ln lock A lock A lock_nested Lm lock_nested Lm So, Lockdep considers this case safe, actually not tho. Byungchul > > -- Steve > > > > > lock_nested L'' with depth n + 1 > > ... ... > > unlock L' unlock L'' > > unlock A unlock A > > unlock L unlock L'
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