linux-kernel - Re: [PATCH 1/4] module: implement module_inhibit

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Date:	Wed, 26 Sep 2007 10:39:06 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <htejun@...il.com>
cc:	Jonathan Corbet <corbet@....net>, <ebiederm@...ssion.com>,
	<cornelia.huck@...ibm.com>, <greg@...ah.com>,
	<kay.sievers@...y.org>, <linux-kernel@...r.kernel.org>,
	<rusty@...tcorp.com.au>
Subject: Re: [PATCH 1/4] module: implement module_inhibit_unload()

On Wed, 26 Sep 2007, Tejun Heo wrote:

> >> Hmmm... I might be missing something here.  Who else can wake up a
> >> thread in uninterruptible sleep?
> > 
> > In principle, anything can.  There has never been any guarantee in the 
> > kernel that a task sleeping on a waitqueue will remain asleep until 
> > the waitqueue is signalled.  That's part of the reason why things like 
> > __wait_event() are coded as loops.
> 
> Hmmm... I always thought the queue was because the condition can change
> inbetween waking up and actually running.  For example, if the condition
> is !(queue empty), another task can enter the critical section and
> consume the element which triggered wake up before the woken up task do.

That's the other part of the reason for using a loop.  :-)

Alan Stern

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