[PATCH v1] [mm] Set page->slab_cache for every page allocated for a kmem_cache.

[Alexander Potapenko]

It's reasonable to rely on the fact that for every page allocated for a
kmem_cache the |slab_cache| field points to that cache. Without that it's
hard to figure out which cache does an allocated object belong to.

Fixes: 55834c59098d0c5a97b0f324 ("mm: kasan: initial memory quarantine
implementation")
Signed-off-by: Alexander Potapenko <gli...@google.com>
---
 mm/slab.c | 7 ++++++-
 mm/slub.c | 8 +++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index cc8bbc1..ac6c251 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2703,8 +2703,13 @@ static void slab_put_obj(struct kmem_cache *cachep,
 static void slab_map_pages(struct kmem_cache *cache, struct page *page,
                           void *freelist)
 {
-       page->slab_cache = cache;
+       int i, nr_pages;
+       char *start = page_address(page);
+
        page->freelist = freelist;
+       nr_pages = (1 << cache->gfporder);
+       for (i = 0; i < nr_pages; i++)
+               virt_to_page(start + PAGE_SIZE * i)->slab_cache = cache;
 }
 
 /*
diff --git a/mm/slub.c b/mm/slub.c
index 825ff45..fc75ddb 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1411,7 +1411,7 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
        struct kmem_cache_order_objects oo = s->oo;
        gfp_t alloc_gfp;
        void *start, *p;
-       int idx, order;
+       int idx, order, i, pages;
 
        flags &= gfp_allowed_mask;
 
@@ -1442,9 +1442,9 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
                stat(s, ORDER_FALLBACK);
        }
 
+       pages = 1 << oo_order(oo);
        if (kmemcheck_enabled &&
            !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
-               int pages = 1 << oo_order(oo);
 
                kmemcheck_alloc_shadow(page, oo_order(oo), alloc_gfp, node);
 
@@ -1461,13 +1461,15 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
        page->objects = oo_objects(oo);
 
        order = compound_order(page);
-       page->slab_cache = s;
        __SetPageSlab(page);
        if (page_is_pfmemalloc(page))
                SetPageSlabPfmemalloc(page);
 
        start = page_address(page);
 
+       for (i = 0; i < pages; i++)
+               virt_to_page(start + PAGE_SIZE * i)->slab_cache = s;
+
        if (unlikely(s->flags & SLAB_POISON))
                memset(start, POISON_INUSE, PAGE_SIZE << order);
 
-- 
2.8.0.rc3.226.g39d4020