diff options
| -rw-r--r-- | include/linux/slub_def.h | 25 | ||||
| -rw-r--r-- | mm/slub.c | 26 |
2 files changed, 35 insertions, 16 deletions
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h index 0764c829d967..a0ad37463d62 100644 --- a/include/linux/slub_def.h +++ b/include/linux/slub_def.h @@ -70,11 +70,8 @@ extern struct kmem_cache kmalloc_caches[KMALLOC_SHIFT_HIGH + 1]; */ static inline int kmalloc_index(size_t size) { - /* - * We should return 0 if size == 0 but we use the smallest object - * here for SLAB legacy reasons. - */ - WARN_ON_ONCE(size == 0); + if (!size) + return 0; if (size > KMALLOC_MAX_SIZE) return -1; @@ -153,13 +150,25 @@ static inline struct kmem_cache *kmalloc_slab(size_t size) #define SLUB_DMA 0 #endif + +/* + * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. + * + * Dereferencing ZERO_SIZE_PTR will lead to a distinct access fault. + * + * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can. + * Both make kfree a no-op. + */ +#define ZERO_SIZE_PTR ((void *)16) + + static inline void *kmalloc(size_t size, gfp_t flags) { if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) { struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return ZERO_SIZE_PTR; return kmem_cache_alloc(s, flags); } else @@ -172,7 +181,7 @@ static inline void *kzalloc(size_t size, gfp_t flags) struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return ZERO_SIZE_PTR; return kmem_cache_zalloc(s, flags); } else @@ -188,7 +197,7 @@ static inline void *kmalloc_node(size_t size, gfp_t flags, int node) struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return ZERO_SIZE_PTR; return kmem_cache_alloc_node(s, flags, node); } else diff --git a/mm/slub.c b/mm/slub.c index 51663a3c3c24..c9ab68881b43 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2241,7 +2241,7 @@ void *__kmalloc(size_t size, gfp_t flags) if (s) return slab_alloc(s, flags, -1, __builtin_return_address(0)); - return NULL; + return ZERO_SIZE_PTR; } EXPORT_SYMBOL(__kmalloc); @@ -2252,16 +2252,20 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node) if (s) return slab_alloc(s, flags, node, __builtin_return_address(0)); - return NULL; + return ZERO_SIZE_PTR; } EXPORT_SYMBOL(__kmalloc_node); #endif size_t ksize(const void *object) { - struct page *page = get_object_page(object); + struct page *page; struct kmem_cache *s; + if (object == ZERO_SIZE_PTR) + return 0; + + page = get_object_page(object); BUG_ON(!page); s = page->slab; BUG_ON(!s); @@ -2293,7 +2297,13 @@ void kfree(const void *x) struct kmem_cache *s; struct page *page; - if (!x) + /* + * This has to be an unsigned comparison. According to Linus + * some gcc version treat a pointer as a signed entity. Then + * this comparison would be true for all "negative" pointers + * (which would cover the whole upper half of the address space). + */ + if ((unsigned long)x <= (unsigned long)ZERO_SIZE_PTR) return; page = virt_to_head_page(x); @@ -2398,12 +2408,12 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags) void *ret; size_t ks; - if (unlikely(!p)) + if (unlikely(!p || p == ZERO_SIZE_PTR)) return kmalloc(new_size, flags); if (unlikely(!new_size)) { kfree(p); - return NULL; + return ZERO_SIZE_PTR; } ks = ksize(p); @@ -2652,7 +2662,7 @@ void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, void *caller) struct kmem_cache *s = get_slab(size, gfpflags); if (!s) - return NULL; + return ZERO_SIZE_PTR; return slab_alloc(s, gfpflags, -1, caller); } @@ -2663,7 +2673,7 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t gfpflags, struct kmem_cache *s = get_slab(size, gfpflags); if (!s) - return NULL; + return ZERO_SIZE_PTR; return slab_alloc(s, gfpflags, node, caller); } |