Hi Namhyung,
On Wed, Feb 29, 2012 at 05:54:34PM +0900, 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
>i 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 <sangseok.lee@xxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung.kim@xxxxxxx>
I read this thread and I feel the we don't reach right point.
I think it's not a compound page problem.
We can face above problem where we allocates big order page without __GFP_COMP
and free middle page of it.
Fortunately, We can catch such a problem by put_page_testzero in __free_pages
if you enable CONFIG_DEBUG_VM.
Did you tried that with CONFIG_DEBUG_VM?
> ---
> 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
>
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