From: "Theodore Ts'o" <tytso@mit.edu>
To: Byungchul Park <byungchul.park@lge.com>
Cc: hamohammed.sa@gmail.com, jack@suse.cz, peterz@infradead.org,
daniel.vetter@ffwll.ch, amir73il@gmail.com, david@fromorbit.com,
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linux-kernel@vger.kernel.org, penberg@kernel.org,
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akpm@linux-foundation.org, torvalds@linux-foundation.org
Subject: Re: Report 2 in ext4 and journal based on v5.17-rc1
Date: Fri, 4 Mar 2022 22:40:35 -0500 [thread overview]
Message-ID: <YiLbs9rszWXpHm/P@mit.edu> (raw)
In-Reply-To: <20220304032002.GD6112@X58A-UD3R>
On Fri, Mar 04, 2022 at 12:20:02PM +0900, Byungchul Park wrote:
>
> I found a point that the two wait channels don't lead a deadlock in
> some cases thanks to Jan Kara. I will fix it so that Dept won't
> complain it.
I sent my last (admittedly cranky) message before you sent this. I'm
glad you finally understood Jan's explanation. I was trying to tell
you the same thing, but apparently I failed to communicate in a
sufficiently clear manner. In any case, what Jan described is a
fundamental part of how wait queues work, and I'm kind of amazed that
you were able to implement DEPT without understanding it. (But maybe
that is why some of the DEPT reports were completely incomprehensible
to me; I couldn't interpret why in the world DEPT was saying there was
a problem.)
In any case, the thing I would ask is a little humility. We regularly
use lockdep, and we run a huge number of stress tests, throughout each
development cycle.
So if DEPT is issuing lots of reports about apparently circular
dependencies, please try to be open to the thought that the fault is
in DEPT, and don't try to argue with maintainers that their code MUST
be buggy --- but since you don't understand our code, and DEPT must be
theoretically perfect, that it is up to the Maintainers to prove to
you that their code is correct.
I am going to gently suggest that it is at least as likely, if not
more likely, that the failure is in DEPT or your understanding of what
how kernel wait channels and locking works. After all, why would it
be that we haven't found these problems via our other QA practices?
Cheers,
- Ted
next prev parent reply other threads:[~2022-03-05 3:41 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-17 10:57 [PATCH 00/16] DEPT(Dependency Tracker) Byungchul Park
2022-02-17 10:57 ` [PATCH 01/16] llist: Move llist_{head,node} definition to types.h Byungchul Park
2022-02-17 10:57 ` [PATCH 02/16] dept: Implement Dept(Dependency Tracker) Byungchul Park
2022-02-17 15:54 ` Steven Rostedt
2022-02-17 17:36 ` Steven Rostedt
2022-02-18 6:09 ` Byungchul Park
2022-02-17 10:57 ` [PATCH 03/16] dept: Embed Dept data in Lockdep Byungchul Park
2022-02-17 10:57 ` [PATCH 04/16] dept: Apply Dept to spinlock Byungchul Park
2022-02-17 10:57 ` [PATCH 05/16] dept: Apply Dept to mutex families Byungchul Park
2022-02-17 10:57 ` [PATCH 06/16] dept: Apply Dept to rwlock Byungchul Park
2022-02-17 10:57 ` [PATCH 07/16] dept: Apply Dept to wait_for_completion()/complete() Byungchul Park
2022-02-17 10:57 ` [PATCH 08/16] dept: Apply Dept to seqlock Byungchul Park
2022-02-17 10:57 ` [PATCH 09/16] dept: Apply Dept to rwsem Byungchul Park
2022-02-17 10:57 ` [PATCH 10/16] dept: Add proc knobs to show stats and dependency graph Byungchul Park
2022-02-17 15:55 ` Steven Rostedt
2022-02-17 10:57 ` [PATCH 11/16] dept: Introduce split map concept and new APIs for them Byungchul Park
2022-02-17 10:57 ` [PATCH 12/16] dept: Apply Dept to wait/event of PG_{locked, writeback} Byungchul Park
2022-02-17 10:57 ` [PATCH 13/16] dept: Apply SDT to swait Byungchul Park
2022-02-17 10:57 ` [PATCH 14/16] dept: Apply SDT to wait(waitqueue) Byungchul Park
2022-02-17 10:57 ` [PATCH 15/16] locking/lockdep, cpu/hotplus: Use a weaker annotation in AP thread Byungchul Park
2022-02-17 10:57 ` [PATCH 16/16] dept: Distinguish each syscall context from another Byungchul Park
2022-02-17 11:10 ` Report 1 in ext4 and journal based on v5.17-rc1 Byungchul Park
2022-02-17 11:10 ` Report 2 " Byungchul Park
2022-02-21 19:02 ` Jan Kara
2022-02-23 0:35 ` Byungchul Park
2022-02-23 14:48 ` Jan Kara
2022-02-24 1:11 ` Byungchul Park
2022-02-24 10:22 ` Jan Kara
2022-02-28 9:28 ` Byungchul Park
2022-02-28 10:14 ` Jan Kara
2022-02-28 21:25 ` Theodore Ts'o
2022-03-03 1:36 ` Byungchul Park
2022-03-03 1:00 ` Byungchul Park
2022-03-03 2:32 ` Theodore Ts'o
2022-03-03 5:23 ` Byungchul Park
2022-03-03 14:36 ` Theodore Ts'o
2022-03-04 0:42 ` Byungchul Park
2022-03-05 3:26 ` Theodore Ts'o
2022-03-05 14:15 ` Byungchul Park
2022-03-05 15:05 ` Joel Fernandes
2022-03-07 2:43 ` Byungchul Park
2022-03-04 3:20 ` Byungchul Park
2022-03-05 3:40 ` Theodore Ts'o [this message]
2022-03-05 14:55 ` Byungchul Park
2022-03-05 15:12 ` Reimar Döffinger
2022-03-06 3:30 ` Theodore Ts'o
2022-03-06 10:51 ` Byungchul Park
2022-03-06 14:19 ` Theodore Ts'o
2022-03-10 1:45 ` Byungchul Park
2022-03-03 9:54 ` Jan Kara
2022-03-04 1:56 ` Byungchul Park
2022-02-17 13:27 ` Report 1 " Matthew Wilcox
2022-02-18 0:41 ` Byungchul Park
2022-02-22 8:27 ` Jan Kara
2022-02-23 1:40 ` Byungchul Park
2022-02-23 3:30 ` Byungchul Park
2022-02-17 15:51 ` [PATCH 00/16] DEPT(Dependency Tracker) Theodore Ts'o
2022-02-17 17:00 ` Steven Rostedt
2022-02-17 17:06 ` Matthew Wilcox
2022-02-19 10:05 ` Byungchul Park
2022-02-18 4:19 ` Theodore Ts'o
2022-02-19 10:34 ` Byungchul Park
2022-02-19 10:18 ` Byungchul Park
2022-02-19 9:54 ` Byungchul Park
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