2012-02-29 08:34:04

by Namhyung Kim

Subject: [PATCH -next] slub: set PG_slab on all of slab pages

Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
call free_pages() incorrectly on a object in a tail page, she will get
confused with the undefined result. Setting the flag would help her by
emitting a warning on bad_page() in such a case.

Reported-by: Sangseok Lee <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
---
mm/slub.c | 12 ++++++++++--
1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 33bab2aca882..575baacbec9b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1287,6 +1287,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
struct page *page;
struct kmem_cache_order_objects oo = s->oo;
gfp_t alloc_gfp;
+ int i;

flags &= gfp_allowed_mask;

@@ -1320,6 +1321,9 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
if (!page)
return NULL;

+ for (i = 0; i < 1 << oo_order(oo); i++)
+ __SetPageSlab(page + i);
+
if (kmemcheck_enabled
&& !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
int pages = 1 << oo_order(oo);
@@ -1369,7 +1373,6 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)

inc_slabs_node(s, page_to_nid(page), page->objects);
page->slab = s;
- page->flags |= 1 << PG_slab;

start = page_address(page);

@@ -1396,6 +1399,7 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
{
int order = compound_order(page);
int pages = 1 << order;
+ int i;

if (kmem_cache_debug(s)) {
void *p;
@@ -1413,7 +1417,11 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
-pages);

- __ClearPageSlab(page);
+ for (i = 0; i < pages; i++) {
+ BUG_ON(!PageSlab(page + i));
+ __ClearPageSlab(page + i);
+ }
+
reset_page_mapcount(page);
if (current->reclaim_state)
current->reclaim_state->reclaimed_slab += pages;
--
1.7.9

2012-02-29 15:31:15

by Christoph Lameter (Ampere)

Subject: Re: [PATCH -next] slub: set PG_slab on all of slab pages

On Wed, 29 Feb 2012, Namhyung Kim wrote:

> Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
> call free_pages() incorrectly on a object in a tail page, she will get
> confused with the undefined result. Setting the flag would help her by
> emitting a warning on bad_page() in such a case.

NAK

You cannot free a tail page of a compound higher order page independently.
You must free the whole compound.