Commit 489a744e authored by Danilo Krummrich's avatar Danilo Krummrich Committed by Andrew Morton
Browse files

mm: krealloc: clarify valid usage of __GFP_ZERO 

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.

Link: https://lkml.kernel.org/r/20240812223707.32049-2-dakr@kernel.org


Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 1a83a716

include/linux/slab.h

+10 −0
Original line number Diff line number Diff line
@@ -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,

mm/slab_common.c

+18 −2
Original line number Diff line number Diff line
@@ -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)