linux-kernel - Re: [PATCH] hugetlb: fix resv

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Date:	Tue, 22 May 2012 16:05:02 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	aarcange@...hat.com, kosaki.motohiro@...fujitsu.com,
	hughd@...gle.com, rientjes@...gle.com, adobriyan@...il.com,
	mel@....ul.ie
Subject: Re: [PATCH] hugetlb: fix resv_map leak in error path

On Tue, 22 May 2012, Andrew Morton wrote:

> On Mon, 21 May 2012 13:28:14 -0700
> Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
>
> > When called for anonymous (non-shared) mappings,
> > hugetlb_reserve_pages() does a resv_map_alloc().  It depends on
> > code in hugetlbfs's vm_ops->close() to release that allocation.
> >
> > However, in the mmap() failure path, we do a plain unmap_region()
> > without the remove_vma() which actually calls vm_ops->close().
> >
> > This is a decent fix.  This leak could get reintroduced if
> > new code (say, after hugetlb_reserve_pages() in
> > hugetlbfs_file_mmap()) decides to return an error.  But, I think
> > it would have to unroll the reservation anyway.
>
> How far back does this bug go?  The patch applies to 3.4 but gets
> rejects in 3.3 and earlier.

The earliest that I have seen it on was 2.6.32. I have rediffed the patch
against 2.6.32 and 3.2.0.

----

>From dave@...ux.vnet.ibm.com Fri May 18 13:50:17 2012
Date: Fri, 18 May 2012 11:46:30 -0700
From: Dave Hansen <dave@...ux.vnet.ibm.com>
To: cl@...ux.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, aarcange@...hat.com, kosaki.motohiro@...fujitsu.com, hughd@...gle.com, rientjes@...gle.com, adobriyan@...il.com, akpm@...ux-foundation.org, mel@....ul.ie, Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: [RFC][PATCH] hugetlb: fix resv_map leak in error path


When called for anonymous (non-shared) mappings,
hugetlb_reserve_pages() does a resv_map_alloc().  It depends on
code in hugetlbfs's vm_ops->close() to release that allocation.

However, in the mmap() failure path, we do a plain unmap_region()
without the remove_vma() which actually calls vm_ops->close().

This is a decent fix.  This leak could get reintroduced if
new code (say, after hugetlb_reserve_pages() in
hugetlbfs_file_mmap()) decides to return an error.  But, I think
it would have to unroll the reservation anyway.

This hasn't been extensively tested.  Pretty much compile and
boot tested along with Christoph's test case.

Comments?


Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>
---

 mm/hugetlb.c |   28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

Index: linux-3.2.0/mm/hugetlb.c
===================================================================
--- linux-3.2.0.orig/mm/hugetlb.c	2012-01-04 17:55:44.000000000 -0600
+++ linux-3.2.0/mm/hugetlb.c	2012-05-22 03:32:37.760054550 -0500
@@ -2068,6 +2068,15 @@ static void hugetlb_vm_op_open(struct vm
 		kref_get(&reservations->refs);
 }

+static void resv_map_put(struct vm_area_struct *vma)
+{
+	struct resv_map *reservations = vma_resv_map(vma);
+
+	if (!reservations)
+		return;
+	kref_put(&reservations->refs, resv_map_release);
+}
+
 static void hugetlb_vm_op_close(struct vm_area_struct *vma)
 {
 	struct hstate *h = hstate_vma(vma);
@@ -2083,7 +2092,7 @@ static void hugetlb_vm_op_close(struct v
 		reserve = (end - start) -
 			region_count(&reservations->regions, start, end);

-		kref_put(&reservations->refs, resv_map_release);
+		resv_map_put(vma);

 		if (reserve) {
 			hugetlb_acct_memory(h, -reserve);
@@ -2883,12 +2892,16 @@ int hugetlb_reserve_pages(struct inode *
 		set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
 	}

-	if (chg < 0)
-		return chg;
+	if (chg < 0) {
+		ret = chg;
+		goto out_err;
+	}

 	/* There must be enough filesystem quota for the mapping */
-	if (hugetlb_get_quota(inode->i_mapping, chg))
-		return -ENOSPC;
+	if (hugetlb_get_quota(inode->i_mapping, chg)) {
+		ret = -ENOSPC;
+		goto out_err;
+	}

 	/*
 	 * Check enough hugepages are available for the reservation.
@@ -2897,7 +2910,7 @@ int hugetlb_reserve_pages(struct inode *
 	ret = hugetlb_acct_memory(h, chg);
 	if (ret < 0) {
 		hugetlb_put_quota(inode->i_mapping, chg);
-		return ret;
+		goto out_err;
 	}

 	/*
@@ -2914,6 +2927,9 @@ int hugetlb_reserve_pages(struct inode *
 	if (!vma || vma->vm_flags & VM_MAYSHARE)
 		region_add(&inode->i_mapping->private_list, from, to);
 	return 0;
+out_err:
+	resv_map_put(vma);
+	return ret;
 }

 void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)

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