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SubjectRe: [PATCHv4] driver core/platform: don't leak memory allocated for dma_mask
On Mon, Jan 27, 2014 at 11:05:52AM +0100, Yann Droneaud wrote:
> Since commit 01dcc60a7cb8, platform_device_register_full() is
> available to allocate and register a platform device.
>
> If a dma_mask is provided as part of platform_device_info,
> platform_device_register_full() allocate memory for a u64 using
> kmalloc().
>
> A comment in the code state that "[t]his memory isn't freed when the
> device is put".
>
> It's never a good thing to leak memory, but there's only very few
> users of platform_device_info's dma_mask, and those are mostly
> "static" devices that are not going to be plugged/unplugged often.
>
> So memory leak is not really an issue, but allocating 8 bytes through
> kmalloc() seems overkill.
>
> And it's a pity to have to allocate 8 bytes for the dma_mask while up
> to 7 bytes are wasted at the end of struct platform_object in the form
> of padding after name field: unfortunately this padding is not used
> when allocating the memory to hold the name.
>
> To address theses issues, this patch adds dma_mask to platform_object
> struct so that it is always allocated for all struct platform_device
> allocated through platform_device_alloc() or platform_device_register_full().
> And since it's within struct platform_object, dma_mask won't be leaked
> anymore when struct platform_device got released. Storage for dma_mask
> is added almost for free by removing the padding at the end of struct
> platform_object.
>
> Padding at the end of the structure is removed by making name a C99
> flexible array member (eg. a zero sized array). To handle this change,
> memory allocation is updated to take care of allocating an additional
> byte for the NUL terminating character.
>
> No more memory leak, no small allocation, no byte wasted and
> a slight reduction in code size.
>
> Built on Fedora 20, using GCC 4.8, for ARM, i386, x86_64 and PPC64
> architectures, the size of the object file and the data structure layout
> are updated as follow, produced with commands:
>
> $ size drivers/base/platform.o
> $ pahole drivers/base/platform.o \
> --recursive \
> --class_name device,pdev_archdata,platform_device,platform_object
>
> --- size+pahole.next-20140124
> +++ size+pahole.next-20140124+
> @@ -1,5 +1,5 @@
> text data bss dec hex filename
> - 5616 472 32 6120 17e8 obj-arm/drivers/base/platform.o
> + 5572 472 32 6076 17bc obj-arm/drivers/base/platform.o
> struct device {
> struct device * parent; /* 0 4 */
> struct device_private * p; /* 4 4 */
> @@ -77,15 +77,15 @@ struct platform_object {
> /* XXX last struct has 4 bytes of padding */
>
> /* --- cacheline 6 boundary (384 bytes) --- */
> - char name[1]; /* 384 1 */
> + u64 dma_mask; /* 384 8 */
> + char name[0]; /* 392 0 */
>
> - /* size: 392, cachelines: 7, members: 2 */
> - /* padding: 7 */
> + /* size: 392, cachelines: 7, members: 3 */
> /* paddings: 1, sum paddings: 4 */
> /* last cacheline: 8 bytes */
> };
>
> text data bss dec hex filename
> - 6007 532 32 6571 19ab obj-i386/drivers/base/platform.o
> + 5943 532 32 6507 196b obj-i386/drivers/base/platform.o
> struct device {
> struct device * parent; /* 0 4 */
> struct device_private * p; /* 4 4 */
> @@ -161,14 +161,14 @@ struct platform_device {
> struct platform_object {
> struct platform_device pdev; /* 0 392 */
> /* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */
> - char name[1]; /* 392 1 */
> + u64 dma_mask; /* 392 8 */
> + char name[0]; /* 400 0 */
>
> - /* size: 396, cachelines: 7, members: 2 */
> - /* padding: 3 */
> - /* last cacheline: 12 bytes */
> + /* size: 400, cachelines: 7, members: 3 */
> + /* last cacheline: 16 bytes */
> };
>
> text data bss dec hex filename
> - 8851 2112 48 11011 2b03 obj-ppc64/drivers/base/platform.o
> + 8787 2104 48 10939 2abb obj-ppc64/drivers/base/platform.o
> struct device {
> struct device * parent; /* 0 8 */
> struct device_private * p; /* 8 8 */
> @@ -256,14 +256,14 @@ struct platform_device {
> struct platform_object {
> struct platform_device pdev; /* 0 728 */
> /* --- cacheline 11 boundary (704 bytes) was 24 bytes ago --- */
> - char name[1]; /* 728 1 */
> + u64 dma_mask; /* 728 8 */
> + char name[0]; /* 736 0 */
>
> - /* size: 736, cachelines: 12, members: 2 */
> - /* padding: 7 */
> + /* size: 736, cachelines: 12, members: 3 */
> /* last cacheline: 32 bytes */
> };
>
> text data bss dec hex filename
> - 7100 960 48 8108 1fac obj-x86_64/drivers/base/platform.o
> + 7020 960 48 8028 1f5c obj-x86_64/drivers/base/platform.o
> struct device {
> struct device * parent; /* 0 8 */
> struct device_private * p; /* 8 8 */
> @@ -350,9 +350,9 @@ struct platform_device {
> struct platform_object {
> struct platform_device pdev; /* 0 712 */
> /* --- cacheline 11 boundary (704 bytes) was 8 bytes ago --- */
> - char name[1]; /* 712 1 */
> + u64 dma_mask; /* 712 8 */
> + char name[0]; /* 720 0 */
>
> - /* size: 720, cachelines: 12, members: 2 */
> - /* padding: 7 */
> + /* size: 720, cachelines: 12, members: 3 */
> /* last cacheline: 16 bytes */
> };
>
> Changes from v3 [1]:
> - fixed commit message so that git am doesn't fail.
>
> Changes from v2 [2]:
> - move 'dma_mask' to platform_object so that it's always
> allocated and won't leak on release; remove all previously
> added support functions.
> - use C99 flexible array member for 'name' to remove padding
> at the end of platform_object.
>
> Changes from v1 [3]:
> - remove unneeded kfree() from error path
> - add reference to author/commit adding allocation of dmamask
>
> Changes from v0 [4]:
> - small rewrite to squeeze the patch to a bare minimal
>
> [1] http://lkml.kernel.org/r/1390771138-28348-1-git-send-email-ydroneaud@opteya.com
> https://patchwork.kernel.org/patch/3540081/
>
> [2] http://lkml.kernel.org/r/1389683909-17495-1-git-send-email-ydroneaud@opteya.com
> https://patchwork.kernel.org/patch/3484411/
>
> [3] http://lkml.kernel.org/r/1389649085-7365-1-git-send-email-ydroneaud@opteya.com
> https://patchwork.kernel.org/patch/3480961/
>
> [4] http://lkml.kernel.org/r/1386886207-2735-1-git-send-email-ydroneaud@opteya.com
>
> Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
> ---
> Hi,
>
> I've fixed the commit message to move the diff on pahole
> outside of the scope of git am.

Uwe, can I get your review of this?

thanks,

greg k-h
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