linux-kernel - Re: workqueue deadlock

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Message-ID: <20061209102652.GA16607@elte.hu>
Date:	Sat, 9 Dec 2006 11:26:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	vatsa@...ibm.com, Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org, Myron Stowe <myron.stowe@...com>,
	Jens Axboe <axboe@...nel.dk>, Dipankar <dipankar@...ibm.com>,
	Gautham shenoy <ego@...ibm.com>
Subject: Re: workqueue deadlock


* Andrew Morton <akpm@...l.org> wrote:

> > > +		if (cpu != -1)
> > > +			mutex_lock(&workqueue_mutex);
> > 
> > events/4 thread itself wanting the same mutex above?
> 
> Could do, not sure.  I'm planning on converting all the locking around 
> here to preempt_disable() though.

please at least use an owner-recursive per-CPU lock, not a naked 
preempt_disable()! The concurrency rules for data structures changed via 
preempt_disable() are quite hard to sort out after the fact. 
(preempt_disable() is too opaque, it doesnt attach data structure to 
critical section, like normal locks do.)

	Ingo
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