Messages in this thread Patch in this message | | | Date | Fri, 1 Jun 2007 16:46:50 -0700 (PDT) | From | Christoph Lameter <> | Subject | Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning |
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On Fri, 1 Jun 2007, Linus Torvalds wrote:
> I'm not seeing the path on the freeing side that silently accepts BADPTR. > > It is not ok to derefence BADPTR, but it's obviously ok to _free_ it.
Ok.
> Also, if I read the patch correctly, you _also_ return BADPTR for slabs > that are too large. No? That would be wrong - those need to return NULL > for "out of memory".
A too large alloc is >32MB or MAX_ORDER << PAGE_SIZE. A BUG_ON in kmalloc_slab() will trigger.
Here is the updated patch. It works fine here:
SLUB: Return BADPTR instead of warning for kmalloc(0)
Remove the WARN_ON_ONCE and simply return BADPTR.
BADPTR can be used legitimately as long as it is not dereferenced. Can even be freed.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
--- include/linux/slub_def.h | 18 ++++++++---------- mm/slub.c | 10 +++++----- 2 files changed, 13 insertions(+), 15 deletions(-)
Index: slub/include/linux/slub_def.h =================================================================== --- slub.orig/include/linux/slub_def.h 2007-06-01 16:19:36.000000000 -0700 +++ slub/include/linux/slub_def.h 2007-06-01 16:43:57.000000000 -0700 @@ -12,6 +12,8 @@ #include <linux/kobject.h> #include <linux/log2.h> +#define BADPTR ((void *)16) + struct kmem_cache_node { spinlock_t list_lock; /* Protect partial list and nr_partial */ unsigned long nr_partial; @@ -74,13 +76,9 @@ extern struct kmem_cache kmalloc_caches[ */ static inline int kmalloc_index(size_t size) { - /* - * We should return 0 if size == 0 (which would result in the - * kmalloc caller to get NULL) but we use the smallest object - * here for legacy reasons. Just issue a warning so that - * we can discover locations where we do 0 sized allocations. - */ - WARN_ON_ONCE(size == 0); + + if (!size) + return 0; if (size > KMALLOC_MAX_SIZE) return -1; @@ -133,7 +131,7 @@ static inline void *kmalloc(size_t size, struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return BADPTR; return kmem_cache_alloc(s, flags); } else @@ -146,7 +144,7 @@ static inline void *kzalloc(size_t size, struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return BADPTR; return kmem_cache_zalloc(s, flags); } else @@ -162,7 +160,7 @@ static inline void *kmalloc_node(size_t struct kmem_cache *s = kmalloc_slab(size); if (!s) - return NULL; + return BADPTR; return kmem_cache_alloc_node(s, flags, node); } else Index: slub/mm/slub.c =================================================================== --- slub.orig/mm/slub.c 2007-06-01 16:21:00.000000000 -0700 +++ slub/mm/slub.c 2007-06-01 16:43:27.000000000 -0700 @@ -2286,7 +2286,7 @@ void *__kmalloc(size_t size, gfp_t flags if (s) return slab_alloc(s, flags, -1, __builtin_return_address(0)); - return NULL; + return BADPTR; } EXPORT_SYMBOL(__kmalloc); @@ -2297,7 +2297,7 @@ void *__kmalloc_node(size_t size, gfp_t if (s) return slab_alloc(s, flags, node, __builtin_return_address(0)); - return NULL; + return BADPTR; } EXPORT_SYMBOL(__kmalloc_node); #endif @@ -2338,7 +2338,7 @@ void kfree(const void *x) struct kmem_cache *s; struct page *page; - if (!x) + if (!x || x == BADPTR) return; page = virt_to_head_page(x); @@ -2707,7 +2707,7 @@ void *__kmalloc_track_caller(size_t size struct kmem_cache *s = get_slab(size, gfpflags); if (!s) - return NULL; + return BADPTR; return slab_alloc(s, gfpflags, -1, caller); } @@ -2718,7 +2718,7 @@ void *__kmalloc_node_track_caller(size_t struct kmem_cache *s = get_slab(size, gfpflags); if (!s) - return NULL; + return BADPTR; return slab_alloc(s, gfpflags, node, caller); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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