The patch titled
Subject: mm: krealloc: clarify valid usage of __GFP_ZERO
has been added to the -mm mm-unstable branch. Its filename is
mm-krealloc-clarify-valid-usage-of-__gfp_zero.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-krealloc-clarify-valid-usage-of-__gfp_zero.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Danilo Krummrich <dakr@xxxxxxxxxx>
Subject: mm: krealloc: clarify valid usage of __GFP_ZERO
Date: Tue, 13 Aug 2024 00:34:35 +0200
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@xxxxxxxxxx
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/slab.h | 10 ++++++++++
mm/slab_common.c | 20 ++++++++++++++++++--
2 files changed, 28 insertions(+), 2 deletions(-)
--- a/include/linux/slab.h~mm-krealloc-clarify-valid-usage-of-__gfp_zero
+++ a/include/linux/slab.h
@@ -733,6 +733,16 @@ static inline __alloc_size(1, 2) void *k
* @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,
--- a/mm/slab_common.c~mm-krealloc-clarify-valid-usage-of-__gfp_zero
+++ a/mm/slab_common.c
@@ -1301,11 +1301,27 @@ __do_krealloc(const void *p, size_t new_
* @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)
_
Patches currently in -mm which might be from dakr@xxxxxxxxxx are
mm-vmalloc-implement-vrealloc.patch
mm-vmalloc-implement-vrealloc-fix.patch
mm-vmalloc-implement-vrealloc-fix-2.patch
mm-vmalloc-implement-vrealloc-fix-3.patch
mm-vmalloc-implement-vrealloc-fix-4.patch
mm-kvmalloc-align-kvrealloc-with-krealloc.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix-2.patch
mm-kvmalloc-align-kvrealloc-with-krealloc-fix-3.patch
mm-krealloc-consider-spare-memory-for-__gfp_zero.patch
mm-krealloc-clarify-valid-usage-of-__gfp_zero.patch
