linux-kernel - Re: [PATCH 1/2] workqueue: debug flushing deadlocks with lockdep

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Message-ID: <20070705145243.GA189@tv-sign.ru>
Date:	Thu, 5 Jul 2007 18:52:43 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Johannes Berg <johannes@...solutions.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/2] workqueue: debug flushing deadlocks with lockdep

On 07/05, Ingo Molnar wrote:
> 
> * Oleg Nesterov <oleg@...sign.ru> wrote:
> 
> > OTOH. Perhaps we can can forbid such a behaviour? Andrew, do you know 
> > any good example of "keventd trying to flush its own queue" ?
> 
> i'd prefer to make the API a little bit stricter: such recursion is 
> nasty. Btw., what mechanism prevents the second instance of 
> run_workqueue() calling into a work->func() again?

Nothing. work->func() can re-schedule itself and then call flush_workqueue().
We have a "morton gets to eat his hat" check in run_workqueue() though.

So I agree with you, such recursion is indeed bad. Can we forbid this?
In that case this patch is even more perfect :)

Oleg.

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