mm: slab: provide krealloc_array()

When allocating an array of elements, users should check for
multiplication overflow or preferably use one of the provided helpers
like: kmalloc_array().

There's no krealloc_array() counterpart but there are many users who use
regular krealloc() to reallocate arrays.  Let's provide an actual
krealloc_array() implementation.

While at it: add some documentation regarding krealloc.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Bartosz Golaszewski <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Christian Knig <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: David Airlie <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Gustavo Padovan <[email protected]>
Cc: James Morse <[email protected]>
Cc: Jaroslav Kysela <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Linus Walleij <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: "Michael S . Tsirkin" <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: Takashi Iwai <[email protected]>
Cc: Takashi Iwai <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: Tony Luck <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Documentation/core-api/memory-allocation.rst

@@ -147,6 +147,10 @@ The address of a chunk allocated with `kmalloc` is aligned to at least
 ARCH_KMALLOC_MINALIGN bytes.  For sizes which are a power of two, the
 alignment is also guaranteed to be at least the respective size.
 
+Chunks allocated with kmalloc() can be resized with krealloc(). Similarly
+to kmalloc_array(): a helper for resizing arrays is provided in the form of
+krealloc_array().
+
 For large allocations you can use vmalloc() and vzalloc(), or directly
 request pages from the page allocator. The memory allocated by `vmalloc`
 and related functions is not physically contiguous.

include/linux/slab.h

@@ -592,6 +592,24 @@ static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
 	return __kmalloc(bytes, flags);
 }
 
+/**
+ * krealloc_array - reallocate memory for an array.
+ * @p: pointer to the memory chunk to reallocate
+ * @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)
+ */
+static __must_check inline void *
+krealloc_array(void *p, size_t new_n, size_t new_size, gfp_t flags)
+{
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(new_n, new_size, &bytes)))
+		return NULL;
+
+	return krealloc(p, bytes, flags);
+}
+
 /**
  * kcalloc - allocate memory for an array. The memory is set to zero.
  * @n: number of elements.