linux-ext4 - Re: [PATCH RFC v7 00/23] DEPT(Dependency Tracker)

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Date:   Mon, 16 Jan 2023 10:00:52 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     linux-kernel@...r.kernel.org, damien.lemoal@...nsource.wdc.com,
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Subject: Re: [PATCH RFC v7 00/23] DEPT(Dependency Tracker)

[ Back from travel, so trying to make sense of this series.. ]

On Sun, Jan 8, 2023 at 7:33 PM Byungchul Park <byungchul.park@....com> wrote:
>
> 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. It's done on v6.2-rc2.

Ugh. I hate how this adds random patterns like

        if (timeout == MAX_SCHEDULE_TIMEOUT)
                sdt_might_sleep_strong(NULL);
        else
                sdt_might_sleep_strong_timeout(NULL);
   ...
        sdt_might_sleep_finish();

to various places, it seems so very odd and unmaintainable.

I also recall this giving a fair amount of false positives, are they all fixed?

Anyway, I'd really like the lockdep people to comment and be involved.
We did have a fairly recent case of "lockdep doesn't track page lock
dependencies because it fundamentally cannot" issue, so DEPT might fix
those kinds of missing dependency analysis. See

    https://lore.kernel.org/lkml/00000000000060d41f05f139aa44@google.com/

for some context to that one, but at teh same time I would *really*
want the lockdep people more involved and acking this work.

Maybe I missed the email where you reported on things DEPT has found
(and on the lack of false positives)?

               Linus