linux-ext4 - Re: [PATCH RFC v6 00/21] DEPT(Dependency Tracker)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 9 May 2022 09:16:37 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.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 Sat, May 07, 2022 at 04:20:50PM +0900, Hyeonggon Yoo wrote:
> 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

No.

> wait events). I mean lockdep allows some kind of nested locks but
> DEPT reports them.

You have already asked exactly same question in another thread of
LKML. That time I answered to it but let me explain it again.

---

CASE 1.

   lock L with depth n
   lock_nested L' with depth n + 1
   ...
   unlock L'
   unlock L

This case is allowed by Lockdep.
This case is allowed by DEPT cuz it's not a deadlock.

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
				lock_nested L'' with depth n + 1
   ...				...
   unlock L'			unlock L''
   unlock A			unlock A
   unlock L			unlock L'

Yes. I need to check if the report you shared with me is a true one, but
it's not because DEPT doesn't work with *_nested() APIs.

	Byungchul