linux-kernel - Re: ENOSPC returned by handle_mm

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Message-ID: <alpine.LSU.2.00.1106051339001.8317@sister.anvils>
Date:	Sun, 5 Jun 2011 13:48:55 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Al Viro <viro@...iv.linux.org.uk>
cc:	linux-mm@...ck.org, Mel Gorman <mel@....ul.ie>,
	linux-kernel@...r.kernel.org
Subject: Re: ENOSPC returned by handle_mm_fault()

On Sun, 5 Jun 2011, Al Viro wrote:
> On Sun, Jun 05, 2011 at 12:16:08PM -0700, Hugh Dickins wrote:
> 
> > Good find, news to me.  Interesting uses of -PTR_ERR()!
> 
> You mean, something like the diff below?

Second hunk yes, but first hunk no: there's at least one other place
(hugetlb_reserve_pages) which calls region_chg(), and expects a
conventional -errno return from it; and even if there weren't,
I'd rather not spread these unconventional return values any deeper.

Something more like the one at the bottom I think: okay, it's slightly
tacky to assume the nature of the failure from vma_needs_reservation(),
but we already have two places which do make that assumption.

> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f33bb31..3de23f0 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -125,7 +125,7 @@ static long region_chg(struct list_head *head, long f, long t)
>  	if (&rg->link == head || t < rg->from) {
>  		nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
>  		if (!nrg)
> -			return -ENOMEM;
> +			return -VM_FAULT_OOM;
>  		nrg->from = f;
>  		nrg->to   = f;
>  		INIT_LIST_HEAD(&nrg->link);
> @@ -1036,7 +1036,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  		return ERR_PTR(chg);
>  	if (chg)
>  		if (hugetlb_get_quota(inode->i_mapping, chg))
> -			return ERR_PTR(-ENOSPC);
> +			return ERR_PTR(-VM_FAULT_SIGBUS);
>  
>  	spin_lock(&hugetlb_lock);
>  	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);

Signed-off-by: Hugh Dickins <hughd@...gle.com
---

 mm/hugetlb.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 3.0-rc1/mm/hugetlb.c	2011-05-29 18:42:37.425882575 -0700
+++ linux/mm/hugetlb.c	2011-06-05 13:33:22.795341004 -0700
@@ -1033,10 +1033,10 @@ static struct page *alloc_huge_page(stru
 	 */
 	chg = vma_needs_reservation(h, vma, addr);
 	if (chg < 0)
-		return ERR_PTR(chg);
+		return ERR_PTR(-VM_FAULT_OOM);
 	if (chg)
 		if (hugetlb_get_quota(inode->i_mapping, chg))
-			return ERR_PTR(-ENOSPC);
+			return ERR_PTR(-VM_FAULT_SIGBUS);
 
 	spin_lock(&hugetlb_lock);
 	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
--
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