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UPSTREAM: mm: move obj_to_index to include/linux/slab_def.h

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(Upstream commit 5b7c4148222d7acaa1612e5eec84fc66c88d54f3).

While with SLUB we can actually preassign tags for caches with contructors
and store them in pointers in the freelist, SLAB doesn't allow that since
the freelist is stored as an array of indexes, so there are no pointers to
store the tags.

Instead we compute the tag twice, once when a slab is created before
calling the constructor and then again each time when an object is
allocated with kmalloc.  Tag is computed simply by taking the lowest byte
of the index that corresponds to the object.  However in kasan_kmalloc we
only have access to the objects pointer, so we need a way to find out
which index this object corresponds to.

This patch moves obj_to_index from slab.c to include/linux/slab_def.h to
be reused by KASAN.

Link: http://lkml.kernel.org/r/c02cd9e574cfd93858e43ac94b05e38f891fef64.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Bug: 128674696
Change-Id: I6cb3332ea05e6152ab8de0490171ed5d4947def3
This commit is contained in:
Andrey Konovalov 2018-12-28 00:30:46 -08:00 committed by Alistair Delva
parent f8adce49ea
commit cf9a2eedfd
2 changed files with 13 additions and 13 deletions
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13
include/linux/slab_def.h
View file

@ -104,4 +104,17 @@ static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
return object;
}
/*
* We want to avoid an expensive divide : (offset / cache->size)
* Using the fact that size is a constant for a particular cache,
* we can replace (offset / cache->size) by
* reciprocal_divide(offset, cache->reciprocal_buffer_size)
*/
static inline unsigned int obj_to_index(const struct kmem_cache *cache,
const struct page *page, void *obj)
{
u32 offset = (obj - page->s_mem);
return reciprocal_divide(offset, cache->reciprocal_buffer_size);
}
#endif /* _LINUX_SLAB_DEF_H */

13
mm/slab.c
View file

@ -406,19 +406,6 @@ static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
return page->s_mem + cache->size * idx;
}
/*
* We want to avoid an expensive divide : (offset / cache->size)
* Using the fact that size is a constant for a particular cache,
* we can replace (offset / cache->size) by
* reciprocal_divide(offset, cache->reciprocal_buffer_size)
*/
static inline unsigned int obj_to_index(const struct kmem_cache *cache,
const struct page *page, void *obj)
{
u32 offset = (obj - page->s_mem);
return reciprocal_divide(offset, cache->reciprocal_buffer_size);
}
#define BOOT_CPUCACHE_ENTRIES 1
/* internal cache of cache description objs */
static struct kmem_cache kmem_cache_boot = {