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From: Peter Zijlstra <peterz@infradead.org>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Amir Goldstein <amir73il@gmail.com>,
	Byungchul Park <byungchul.park@lge.com>,
	Dave Chinner <david@fromorbit.com>,
	fstests <fstests@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	mingo@redhat.com, kernel-team@lge.com
Subject: Re: False lockdep completion splats with loop device
Date: Thu, 7 Dec 2017 15:53:25 +0100	[thread overview]
Message-ID: <20171207145325.47bt3wdd3pm4rvxu@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20171207143329.ioir5cx3fzyqpo4g@thunk.org>

On Thu, Dec 07, 2017 at 09:33:29AM -0500, Theodore Ts'o wrote:
> Let me ask a potentially stupid question, Can someone give an example
> of the problem this completion lockdep is actually trying to *catch*.
> The lockdep message is sufficiently confusing it's not even clear what
> *good* it is in the first place.


	lock(A)			lock(A)
	wait_for_completion(C)	complete(C);


> Is there an example of a bug that this lockdep feature hasf actually
> caught in real life, as opposed to false positives?

Yes, it caught a fair bunch of real deadlocks in cpu hotplug, watchdog,
and other places I can't remember.

Here's one in the mm:

  https://lkml.kernel.org/r/20171030152200.ayfnewoqkxbuk4zh@hirez.programming.kicks-ass.net

I have at least one open issue in perf that I've no real idea what to do
about:

  https://lkml.kernel.org/r/20171027153336.GC3857@worktop


Yes lockdep is a pain...

  reply	other threads:[~2017-12-07 14:53 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-05  3:03 False lockdep completion splats with loop device Theodore Ts'o
2017-12-05  5:16 ` Byungchul Park
2017-12-05 15:07   ` Theodore Ts'o
2017-12-05 21:09     ` Dave Chinner
2017-12-06  5:01       ` Byungchul Park
2017-12-06  6:08         ` Dave Chinner
2017-12-06  6:31         ` Amir Goldstein
2017-12-06  7:01           ` Byungchul Park
2017-12-07  2:46             ` Amir Goldstein
2017-12-07  4:18               ` Amir Goldstein
2017-12-07 14:33                 ` Theodore Ts'o
2017-12-07 14:53                   ` Peter Zijlstra [this message]
2017-12-08  1:51                 ` Byungchul Park
2017-12-07 23:59               ` Dave Chinner
2017-12-08  0:13                 ` Al Viro
2017-12-08  8:15                   ` Amir Goldstein
2017-12-08 22:57                     ` Dave Chinner
2017-12-09  8:44                       ` Amir Goldstein
2017-12-09 16:02                         ` Theodore Ts'o
2017-12-09 20:08                           ` Amir Goldstein
2017-12-06  6:23     ` Byungchul Park

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