Date: Thu, 7 May 2015 13:51:18 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: David Hildenbrand <dahi@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, yang.shi@windriver.com,
        bigeasy@linutronix.de, benh@kernel.crashing.org, paulus@samba.org,
        akpm@linux-foundation.org, heiko.carstens@de.ibm.com,
        schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com,
        tglx@linutronix.de, David.Laight@ACULAB.COM, hughd@google.com,
        hocko@suse.cz, ralf@linux-mips.org, herbert@gondor.apana.org.au,
        linux@arm.linux.org.uk, airlied@linux.ie, daniel.vetter@intel.com,
        linux-mm@kvack.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in
 pagefault_disabled
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On Thu, May 07, 2015 at 01:40:30PM +0200, David Hildenbrand wrote:
> But anyhow, opinions seem to differ how to best handle that whole stuff.
> 
> I think a separate counter just makes sense, as we are dealing with two
> different concepts and we don't want to lose the preempt_disable =^ NOP
> for !CONFIG_PREEMPT.
> 
> I also think that
> 
> pagefault_disable()
> rt = copy_from_user()
> pagefault_enable()
> 
> is a valid use case.
> 
> So any suggestions how to continue?


static inline bool __pagefault_disabled(void)
{
	return current->pagefault_disabled;
}

static inline bool pagefault_disabled(void)
{
	return in_atomic() || __pagefault_disabled();
}

And leave the preempt_disable() + pagefault_disable() for now. You're
right in that that is clearest.

If we ever get to the point where that really is an issue, I'll try and
be clever then :-)
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