Properly document that if __GFP_ZERO logic is requested, callers must ensure that, starting with the initial memory allocation, every subsequent call to this API for the same memory allocation is flagged with __GFP_ZERO. Otherwise, it is possible that __GFP_ZERO is not fully honored by this API. Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx> --- Changes in v2: - additionally to what we require callers to do, briefly explain what the implementation does (Andrew) --- include/linux/slab.h | 10 ++++++++++ mm/slab_common.c | 20 ++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index c9cb42203183..2282e67a01c7 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -733,6 +733,16 @@ static inline __alloc_size(1, 2) void *kmalloc_array_noprof(size_t n, size_t siz * @new_n: new number of elements to alloc * @new_size: new size of a single member of the array * @flags: the type of memory to allocate (see kmalloc) + * + * If __GFP_ZERO logic is requested, callers must ensure that, starting with the + * initial memory allocation, every subsequent call to this API for the same + * memory allocation is flagged with __GFP_ZERO. Otherwise, it is possible that + * __GFP_ZERO is not fully honored by this API. + * + * See krealloc_noprof() for further details. + * + * In any case, the contents of the object pointed to are preserved up to the + * lesser of the new and old sizes. */ static inline __realloc_size(2, 3) void * __must_check krealloc_array_noprof(void *p, size_t new_n, diff --git a/mm/slab_common.c b/mm/slab_common.c index cff602cedf8e..1b380eb3b4f2 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -1301,11 +1301,27 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags) * @new_size: how many bytes of memory are required. * @flags: the type of memory to allocate. * - * The contents of the object pointed to are preserved up to the - * lesser of the new and old sizes (__GFP_ZERO flag is effectively ignored). * If @p is %NULL, krealloc() behaves exactly like kmalloc(). If @new_size * is 0 and @p is not a %NULL pointer, the object pointed to is freed. * + * If __GFP_ZERO logic is requested, callers must ensure that, starting with the + * initial memory allocation, every subsequent call to this API for the same + * memory allocation is flagged with __GFP_ZERO. Otherwise, it is possible that + * __GFP_ZERO is not fully honored by this API. + * + * This is the case, since krealloc() only knows about the bucket size of an + * allocation (but not the exact size it was allocated with) and hence + * implements the following semantics for shrinking and growing buffers with + * __GFP_ZERO. + * + * new bucket + * 0 size size + * |--------|----------------| + * | keep | zero | + * + * In any case, the contents of the object pointed to are preserved up to the + * lesser of the new and old sizes. + * * Return: pointer to the allocated memory or %NULL in case of error */ void *krealloc_noprof(const void *p, size_t new_size, gfp_t flags) -- 2.46.0
