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

From: Yann Droneaud <ydroneaud@opteya.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, Yann Droneaud <ydroneaud@opteya.com>
Subject: [PATCH] driver core/platform: don't leak memory allocated for dma_mask
Date: Thu, 12 Dec 2013 23:10:07 +0100	[thread overview]
Message-ID: <1386886207-2735-1-git-send-email-ydroneaud@opteya.com> (raw)

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.

So memory leak is not really an issue, but allocating 8 bytes
through kmalloc() seems overkill, so this patch moves dma_mask
after the platform_device struct, dynamically allocated along
the name buffer.

With dma_mask part of the memory allocated for the platform_device
struct, like name buffer, it will be released with it:
no memory leak, no small allocation.

The draw back is the additional code needed to handle
dma_mask allocation:

Before:
   text	   data	    bss	    dec	    hex	filename
   5927	    532	     32	   6491	   195b	obj-i386/drivers/base/platform.o
   7038	    960	     48	   8046	   1f6e	obj-x86_64/drivers/base/platform.o

After:
   text	   data	    bss	    dec	    hex	filename
   6007	    532	     32	   6571	   19ab	obj-i386/drivers/base/platform.o
   7134	    960	     48	   8142	   1fce	obj-x86_64/drivers/base/platform.o

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
---
 drivers/base/platform.c | 93 +++++++++++++++++++++++++++++++++++--------------
 1 file changed, 67 insertions(+), 26 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 3a94b799f166..95f4cbafe1d7 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -157,7 +157,7 @@ EXPORT_SYMBOL_GPL(platform_add_devices);
 
 struct platform_object {
 	struct platform_device pdev;
-	char name[1];
+	char payload[0];
 };
 
 /**
@@ -186,6 +186,25 @@ static void platform_device_release(struct device *dev)
 	kfree(pa);
 }
 
+static struct platform_object *platform_object_alloc(size_t payload)
+{
+	struct platform_object *pa;
+
+	pa = kzalloc(sizeof(*pa) + payload, GFP_KERNEL);
+
+	return pa;
+}
+
+static void platform_object_init(struct platform_object *pa,
+				 const char *name, int id)
+{
+	pa->pdev.name = name;
+	pa->pdev.id = id;
+	device_initialize(&pa->pdev.dev);
+	pa->pdev.dev.release = platform_device_release;
+	arch_setup_pdev_archdata(&pa->pdev);
+}
+
 /**
  * platform_device_alloc - create a platform device
  * @name: base name of the device we're adding
@@ -198,14 +217,10 @@ 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 = platform_object_alloc(strlen(name) + 1);
 	if (pa) {
-		strcpy(pa->name, name);
-		pa->pdev.name = pa->name;
-		pa->pdev.id = id;
-		device_initialize(&pa->pdev.dev);
-		pa->pdev.dev.release = platform_device_release;
-		arch_setup_pdev_archdata(&pa->pdev);
+		strcpy(pa->payload, name);
+		platform_object_init(pa, pa->payload, id);
 	}
 
 	return pa ? &pa->pdev : NULL;
@@ -213,6 +228,38 @@ struct platform_device *platform_device_alloc(const char *name, int id)
 EXPORT_SYMBOL_GPL(platform_device_alloc);
 
 /**
+ * platform_device_dmamask_alloc - create a platform device suitable to hold a dmamask
+ * @name: base name of the device we're adding
+ * @id: instance id
+ *
+ * Create a platform device object which can have other objects attached
+ * to it, and which will have attached objects freed when it is released.
+ */
+static struct platform_device *platform_device_dmamask_alloc(const char *name,
+							     int id)
+{
+	struct platform_object *pa;
+	const size_t padding = (((offsetof(struct platform_object, payload) +
+				  (__alignof__(u64) - 1)) &
+				 ~(__alignof__(u64) - 1)) -
+				offsetof(struct platform_object, payload));
+
+	pa = platform_object_alloc(padding + sizeof(u64) + strlen(name) + 1);
+	if (pa) {
+		char *payload = pa->payload + padding;
+		strcpy(payload + sizeof(u64), name);
+		/*
+		 * Conceptually dma_mask in struct device should not be a pointer.
+		 * See http://thread.gmane.org/gmane.linux.kernel.pci/9081
+		 */
+		pa->pdev.dev.dma_mask = (void *)payload;
+		platform_object_init(pa, payload + sizeof(u64), id);
+	}
+
+	return pa ? &pa->pdev : NULL;
+}
+
+/**
  * platform_device_add_resources - add resources to a platform device
  * @pdev: platform device allocated by platform_device_alloc to add resources to
  * @res: set of resources that needs to be allocated for the device
@@ -427,29 +474,23 @@ struct platform_device *platform_device_register_full(
 	int ret = -ENOMEM;
 	struct platform_device *pdev;
 
-	pdev = platform_device_alloc(pdevinfo->name, pdevinfo->id);
-	if (!pdev)
-		goto err_alloc;
-
-	pdev->dev.parent = pdevinfo->parent;
-	ACPI_COMPANION_SET(&pdev->dev, pdevinfo->acpi_node.companion);
-
-	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;
+	if (!pdevinfo->dma_mask) {
+		pdev = platform_device_alloc(pdevinfo->name, pdevinfo->id);
+		if (!pdev)
+			goto err_alloc;
+	} else {
+		pdev = platform_device_dmamask_alloc(pdevinfo->name,
+						     pdevinfo->id);
+		if (!pdev)
+			goto err_alloc;
 
 		*pdev->dev.dma_mask = pdevinfo->dma_mask;
 		pdev->dev.coherent_dma_mask = pdevinfo->dma_mask;
 	}
 
+	pdev->dev.parent = pdevinfo->parent;
+	ACPI_COMPANION_SET(&pdev->dev, pdevinfo->acpi_node.companion);
+
 	ret = platform_device_add_resources(pdev,
 			pdevinfo->res, pdevinfo->num_res);
 	if (ret)
-- 
1.8.4.2

