linux-kernel - Re: 2.6.24-rc2-mm1: kcryptd vs lockdep

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Message-ID: <4742F1DE.1090902@redhat.com>
Date:	Tue, 20 Nov 2007 15:40:30 +0100
From:	Milan Broz <mbroz@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Torsten Kaiser <just.for.lkml@...glemail.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Alasdair G Kergon <agk@...hat.com>
Subject: Re: 2.6.24-rc2-mm1: kcryptd vs lockdep

Torsten Kaiser wrote:
> On Nov 19, 2007 10:00 PM, Milan Broz <mbroz@...hat.com> wrote:
>> Torsten Kaiser wrote:
>>> Anything I could try, apart from more boots with slub_debug=F?
> 
> One time it triggered with slub_debug=F, but no additional output.
> With slub_debug=FP I have not seen it again, so I can't say if that
> would yield more info.
> 
>> Please could you try which patch from the dm-crypt series cause this ?
>> (agk-dm-dm-crypt* names.)
>>
>> I suspect agk-dm-dm-crypt-move-bio-submission-to-thread.patch because
>> there is one work struct used subsequently in two threads...
>> (io thread already started while crypt thread is processing lockdep_map
>> after calling f(work)...)
> 
> After reverting only
> agk-dm-dm-crypt-move-bio-submission-to-thread.patch I also have not
> seen the 'held lock freed' message again.

Ok, then I have question: Is the following pseudocode correct
(and problem is in lock validation which checks something
already initialized for another queue) or reusing work_struct
is not permitted from inside called work function ?

(Note comment in code "It is permissible to free the struct
work_struct from inside the function that is called from it".)

struct work_struct work;
struct workqueue_struct *a, *b;

do_b(*work) 
{
	/* do something else */
}

do_a(*work)
{
	/* do something */
	INIT_WORK(&work, do_b);
	queue_work(b, &work);
}


INIT_WORK(&work, do_a);
queue_work(a, &work);

Milan
--
mbroz@...hat.com
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