linux-kernel - Re: [PATCH] mm: mempolicy: turn vma_set_policy() into vma_dup

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Date:	Thu, 11 Jul 2013 15:27:46 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: mempolicy: turn vma_set_policy() into
 vma_dup_policy()

On Thu, 11 Jul 2013, Andrew Morton wrote:

> On Thu, 11 Jul 2013 15:13:03 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:
> 
> > > +int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
> > > +{
> > > +	struct mempolicy *pol = mpol_dup(vma_policy(src));
> > > +
> > > +	if (IS_ERR(pol))
> > > +		return PTR_ERR(pol);
> > 
> > PTR_ERR() returns long, so vma_dup_policy() needs to return long.
> 
> hm, really?  vma_dup_policy() returns an errno and errnos have type "int".
> 
> Arguably it is PTR_ERR() which returns the wrong type...
> 

PTR_ERR() may not imply IS_ERR(), which I believe Rusty is trying to fix 
with his series that fixes up abuses of PTR_ERR().  But I agree that 
vma_dup_policy() can return int because of the IS_ERR() check as written.  

For complete correctness there should probably be a build error if 
MAX_ERRNO cannot fit in an int and then this should do 
return (int)PTR_ERR(pol) to make it clear.
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