[PATCHv4] driver core/platform: don't leak memory allocated for dma_mask

From: Yann Droneaud
Date: Mon Jan 27 2014 - 05:06:26 EST

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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@xxxxxxxxxx
https://patchwork.kernel.org/patch/3540081/

[2] http://lkml.kernel.org/r/1389683909-17495-1-git-send-email-ydroneaud@xxxxxxxxxx
https://patchwork.kernel.org/patch/3484411/

[3] http://lkml.kernel.org/r/1389649085-7365-1-git-send-email-ydroneaud@xxxxxxxxxx
https://patchwork.kernel.org/patch/3480961/

[4] http://lkml.kernel.org/r/1386886207-2735-1-git-send-email-ydroneaud@xxxxxxxxxx

Cc: Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Yann Droneaud <ydroneaud@xxxxxxxxxx>
---
Hi,

I've fixed the commit message to move the diff on pahole
outside of the scope of git am.

Regards.

drivers/base/platform.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index bc78848dd59a..1f6d1e832e03 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -157,7 +157,8 @@ EXPORT_SYMBOL_GPL(platform_add_devices);

struct platform_object {
struct platform_device pdev;
- char name[1];
+ u64 dma_mask;
+ char name[];
};

/**
@@ -193,16 +194,20 @@ static void platform_device_release(struct device *dev)
*
* Create a platform device object which can have other objects attached
* to it, and which will have attached objects freed when it is released.
+ *
+ * The associated struct device will be set up so that its dma_mask field
+ * is a valid pointer to an u64. This pointer must not be free'd manually.
*/
struct platform_device *platform_device_alloc(const char *name, int id)
{
struct platform_object *pa;

- pa = kzalloc(sizeof(struct platform_object) + strlen(name), GFP_KERNEL);
+ pa = kzalloc(sizeof(*pa) + strlen(name) + 1, GFP_KERNEL);
if (pa) {
strcpy(pa->name, name);
pa->pdev.name = pa->name;
pa->pdev.id = id;
+ pa->pdev.dev.dma_mask = &pa->dma_mask;
device_initialize(&pa->pdev.dev);
pa->pdev.dev.release = platform_device_release;
arch_setup_pdev_archdata(&pa->pdev);
@@ -436,16 +441,9 @@ struct platform_device *platform_device_register_full(

if (pdevinfo->dma_mask) {
/*
- * This memory isn't freed when the device is put,
- * I don't have a nice idea for that though. Conceptually
* dma_mask in struct device should not be a pointer.
* See http://thread.gmane.org/gmane.linux.kernel.pci/9081
*/
- pdev->dev.dma_mask =
- kmalloc(sizeof(*pdev->dev.dma_mask), GFP_KERNEL);
- if (!pdev->dev.dma_mask)
- goto err;
-
*pdev->dev.dma_mask = pdevinfo->dma_mask;
pdev->dev.coherent_dma_mask = pdevinfo->dma_mask;
}
@@ -464,7 +462,6 @@ struct platform_device *platform_device_register_full(
if (ret) {
err:
ACPI_COMPANION_SET(&pdev->dev, NULL);
- kfree(pdev->dev.dma_mask);

err_alloc:
platform_device_put(pdev);
--
1.8.5.3

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Next message: Weijie Yang: "[PATCH 5/8] mm/swap: drop useless and bug frontswap_shrink codes"
Previous message: Weijie Yang: "[PATCH 6/8] mm/swap: remove swap_lock to simplify si_swapinfo()"
In reply to: Yann Droneaud: "[PATCHv3] driver core/platform: don't leak memory allocated for dma_mask"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]