[v2,1/8] mm: slab: provide krealloc_array()

Commit Message

Bartosz Golaszewski Nov. 2, 2020, 3:20 p.m. UTC

From: Bartosz Golaszewski <[e-mail]>

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.

Signed-off-by: Bartosz Golaszewski <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
---
 Documentation/core-api/memory-allocation.rst |  4 ++++
 include/linux/slab.h                         | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

Comments

Matthew Wilcox Nov. 2, 2020, 3:41 p.m. UTC | #1

On Mon, Nov 02, 2020 at 04:20:30PM +0100, Bartosz Golaszewski wrote:
> +Chunks allocated with `kmalloc` can be resized with `krealloc`. Similarly
> +to `kmalloc_array`: a helper for resising arrays is provided in the form of
> +`krealloc_array`.

Is there any reason you chose to `do_this` instead of do_this()?  The
automarkup script turns do_this() into a nice link to the documentation
which you're adding below.

Typo 'resising' resizing.

Bartosz Golaszewski Nov. 2, 2020, 3:43 p.m. UTC | #2

On Mon, Nov 2, 2020 at 4:41 PM Matthew Wilcox <[e-mail]> wrote:
>
> On Mon, Nov 02, 2020 at 04:20:30PM +0100, Bartosz Golaszewski wrote:
> > +Chunks allocated with `kmalloc` can be resized with `krealloc`. Similarly
> > +to `kmalloc_array`: a helper for resising arrays is provided in the form of
> > +`krealloc_array`.
>
> Is there any reason you chose to `do_this` instead of do_this()?  The
> automarkup script turns do_this() into a nice link to the documentation
> which you're adding below.
>

No, I just didn't know better. Thanks for bringing this to my attention.

> Typo 'resising' resizing.

Will fix in the next iteration.

Bartosz

Patch

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 4446a1ac36cc..6dc38b40439a 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/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 resising 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.
diff --git a/include/linux/slab.h b/include/linux/slab.h
index dd6897f62010..be4ba5867ac5 100644
--- a/include/linux/slab.h
+++ b/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.