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Date: Tue, 21 May 2013 13:18:18 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep
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On Sun, May 19, 2013 at 07:40:09PM +0300, Michael S. Tsirkin wrote:
> OK I get it. So let me correct myself. The simple code
> that does something like this under a spinlock:
> >       preempt_disable
> >       pagefault_disable
> >       error = copy_to_user
> >       pagefault_enable
> >       preempt_enable
> >
> is not doing anything wrong and should not get a warning,
> as long as error is handled correctly later.
> Right?

Indeed, but I don't get the point of the preempt_{disable,enable}()
here. Why does it have to disable preemption explicitly here? I thought
all you wanted was to avoid the pagefault handler and make it do the
exception table thing; for that pagefault_disable() is sufficient.