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Subject: Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep
From: Steven Rostedt <rostedt@goodmis.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Date: Sun, 19 May 2013 08:34:04 -0400
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Cc: linux-m32r-ja@ml.linux-m32r.org, kvm@vger.kernel.org,
 Peter Zijlstra <peterz@infradead.org>,
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 microblaze-uclinux@itee.uq.edu.au, Chris Metcalf <cmetcalf@tilera.com>,
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On Sun, 2013-05-19 at 12:35 +0300, Michael S. Tsirkin wrote:

> No, I was not assuming that. What I'm trying to say is that a caller
> that does something like this under a spinlock:
> 	preempt_disable
> 	pagefault_disable
> 	error = copy_to_user
> 	pagefault_enable
> 	preempt_enable_no_resched
> 
> is not doing anything wrong and should not get a warning,
> as long as error is handled correctly later.
> Right?
> 

What I see wrong with the above is the preempt_enable_no_resched(). The
only place that should be ever used is right before a schedule(), as you
don't want to schedule twice (once for the preempt_enable() and then
again for the schedule itself).

Remember, in -rt, a spin lock does not disable preemption.

-- Steve