linux-kernel - Re: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might

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Date:	Fri, 5 Dec 2014 12:46:29 +0100
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, schwidefsky@...ibm.com,
	borntraeger@...ibm.com, mst@...hat.com, tglx@...utronix.de,
	David.Laight@...LAB.COM, peterz@...radead.org, hughd@...gle.com,
	hocko@...e.cz
Subject: Re: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in
 might_fault() when pagefaults are disabled

> On Fri, Dec 05, 2014 at 12:18:07PM +0100, David Hildenbrand wrote:
> > -void might_fault(void)
> > +void __might_fault(const char *file, int line)
> >  {
> >  	/*
> >  	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
> > @@ -3710,21 +3710,16 @@ void might_fault(void)
> >  	 */
> >  	if (segment_eq(get_fs(), KERNEL_DS))
> >  		return;
> > -
> > -	/*
> > -	 * it would be nicer only to annotate paths which are not under
> > -	 * pagefault_disable, however that requires a larger audit and
> > -	 * providing helpers like get_user_atomic.
> > -	 */
> > -	if (in_atomic())
> > +	if (unlikely(!pagefault_disabled())) {
> > +		__might_sleep(file, line, 0);
> >  		return;
> > -
> > -	__might_sleep(__FILE__, __LINE__, 0);
> > -
> > +	}
> 
> This should be likely() instead of unlikely(), no?
> I'd rather write this
> 
> 	if (pagefault_disabled())
>  		return;
> 	__might_sleep(file, line, 0);
> 
> and leave the likely stuff completely away.

Makes perfect sense!

Thanks!

David

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