mm-krealloc-clarify-valid-usage-of-__gfp_zero.patch removed from -mm tree

@@ -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,

@@ -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)