[v4,01/11] firmware: raspberrypi: Keep count of all consumers
diff mbox series

Message ID 20201112163630.17177-2-nsaenzjulienne@suse.de
State New, archived
Headers show
Series
  • Raspberry Pi PoE HAT fan support
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Commit Message

Nicolas Saenz Julienne Nov. 12, 2020, 4:36 p.m. UTC
When unbinding the firmware device we need to make sure it has no
consumers left. Otherwise we'd leave them with a firmware handle
pointing at freed memory.

Keep a reference count of all consumers and introduce rpi_firmware_put()
which will permit automatically decrease the reference count upon
unbinding consumer drivers.

Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---

Changes since v3:
- Use kref instead of waiting on refcount

 drivers/firmware/raspberrypi.c             | 37 +++++++++++++++++++---
 include/soc/bcm2835/raspberrypi-firmware.h |  2 ++
 2 files changed, 35 insertions(+), 4 deletions(-)

Comments

Andy Shevchenko Nov. 12, 2020, 5:52 p.m. UTC | #1
On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
<nsaenzjulienne@suse.de> wrote:
>
> When unbinding the firmware device we need to make sure it has no
> consumers left. Otherwise we'd leave them with a firmware handle
> pointing at freed memory.
>
> Keep a reference count of all consumers and introduce rpi_firmware_put()
> which will permit automatically decrease the reference count upon
> unbinding consumer drivers.

...

>  /**
> - * rpi_firmware_get - Get pointer to rpi_firmware structure.
>   * @firmware_node:    Pointer to the firmware Device Tree node.
>   *
> + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> + *
>   * Returns NULL is the firmware device is not ready.
>   */
>  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
>  {
>         struct platform_device *pdev = of_find_device_by_node(firmware_node);
> +       struct rpi_firmware *fw;
>
>         if (!pdev)
>                 return NULL;
>
> -       return platform_get_drvdata(pdev);
> +       fw = platform_get_drvdata(pdev);
> +       if (!fw)
> +               return NULL;
> +
> +       if (!kref_get_unless_zero(&fw->consumers))
> +               return NULL;

Don't we have a more traditional way of doing this, i.e.
try_module_get() coupled with get_device() ?

> +       return fw;
>  }
dmitry.torokhov@gmail.com Nov. 13, 2020, 7:26 a.m. UTC | #2
On Thu, Nov 12, 2020 at 07:52:14PM +0200, Andy Shevchenko wrote:
> On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
> <nsaenzjulienne@suse.de> wrote:
> >
> > When unbinding the firmware device we need to make sure it has no
> > consumers left. Otherwise we'd leave them with a firmware handle
> > pointing at freed memory.
> >
> > Keep a reference count of all consumers and introduce rpi_firmware_put()
> > which will permit automatically decrease the reference count upon
> > unbinding consumer drivers.
> 
> ...
> 
> >  /**
> > - * rpi_firmware_get - Get pointer to rpi_firmware structure.
> >   * @firmware_node:    Pointer to the firmware Device Tree node.
> >   *
> > + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> > + *
> >   * Returns NULL is the firmware device is not ready.
> >   */
> >  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
> >  {
> >         struct platform_device *pdev = of_find_device_by_node(firmware_node);
> > +       struct rpi_firmware *fw;
> >
> >         if (!pdev)
> >                 return NULL;
> >
> > -       return platform_get_drvdata(pdev);
> > +       fw = platform_get_drvdata(pdev);
> > +       if (!fw)
> > +               return NULL;
> > +
> > +       if (!kref_get_unless_zero(&fw->consumers))
> > +               return NULL;
> 
> Don't we have a more traditional way of doing this, i.e.
> try_module_get() coupled with get_device() ?

get_device() will make sure that device is there, but gives no
assurances that device is bound to a driver, so it will not help with
the racy access to firmware via platform_get_drvdata() call.

Thanks.
Nicolas Saenz Julienne Nov. 23, 2020, 5:19 p.m. UTC | #3
On Thu, 2020-11-12 at 23:26 -0800, Dmitry Torokhov wrote:
> On Thu, Nov 12, 2020 at 07:52:14PM +0200, Andy Shevchenko wrote:
> > On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
> > <nsaenzjulienne@suse.de> wrote:
> > > 
> > > When unbinding the firmware device we need to make sure it has no
> > > consumers left. Otherwise we'd leave them with a firmware handle
> > > pointing at freed memory.
> > > 
> > > Keep a reference count of all consumers and introduce rpi_firmware_put()
> > > which will permit automatically decrease the reference count upon
> > > unbinding consumer drivers.
> > 
> > ...
> > 
> > >  /**
> > > - * rpi_firmware_get - Get pointer to rpi_firmware structure.
> > >   * @firmware_node:    Pointer to the firmware Device Tree node.
> > >   *
> > > + * The reference to rpi_firmware has to be released with rpi_firmware_put().
> > > + *
> > >   * Returns NULL is the firmware device is not ready.
> > >   */
> > >  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
> > >  {
> > >         struct platform_device *pdev = of_find_device_by_node(firmware_node);
> > > +       struct rpi_firmware *fw;
> > > 
> > >         if (!pdev)
> > >                 return NULL;
> > > 
> > > -       return platform_get_drvdata(pdev);
> > > +       fw = platform_get_drvdata(pdev);
> > > +       if (!fw)
> > > +               return NULL;
> > > +
> > > +       if (!kref_get_unless_zero(&fw->consumers))
> > > +               return NULL;
> > 

Hi Andy, Dimitry,

> > Don't we have a more traditional way of doing this, i.e.
> > try_module_get() coupled with get_device() ?
> 
> get_device() will make sure that device is there, but gives no
> assurances that device is bound to a driver, so it will not help with
> the racy access to firmware via platform_get_drvdata() call.

I also looked at using get/put_device() just as a means for refcounting (i.e.
replacing fw->consumers), but I can't make it work either. I'd need a way to
hook up into one of the struct device_ktype release() functions. AFAIK it's not
possible for private uses like this.

IIUC the way to do this would be to bypass platform device and create a special
device class/bus for RPi's firmware dependent devices (I could pretty much copy
SCMI's implementation), but I fear that's overkill.

So, for now I'll stick with the kref based implementation, I'll be happy to
change it if you find a better solution. :)

Regards,
Nicolas

Patch
diff mbox series

diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
index 2371d08bdd17..438e17074a97 100644
--- a/drivers/firmware/raspberrypi.c
+++ b/drivers/firmware/raspberrypi.c
@@ -7,6 +7,7 @@ 
  */
 
 #include <linux/dma-mapping.h>
+#include <linux/kref.h>
 #include <linux/mailbox_client.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
@@ -27,6 +28,8 @@  struct rpi_firmware {
 	struct mbox_chan *chan; /* The property channel. */
 	struct completion c;
 	u32 enabled;
+
+	struct kref consumers;
 };
 
 static DEFINE_MUTEX(transaction_lock);
@@ -225,12 +228,27 @@  static void rpi_register_clk_driver(struct device *dev)
 						-1, NULL, 0);
 }
 
+static void rpi_firmware_delete(struct kref *kref)
+{
+	struct rpi_firmware *fw = container_of(kref, struct rpi_firmware,
+					       consumers);
+
+	mbox_free_channel(fw->chan);
+	kfree(fw);
+}
+
+void rpi_firmware_put(struct rpi_firmware *fw)
+{
+	kref_put(&fw->consumers, rpi_firmware_delete);
+}
+EXPORT_SYMBOL_GPL(rpi_firmware_put);
+
 static int rpi_firmware_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct rpi_firmware *fw;
 
-	fw = devm_kzalloc(dev, sizeof(*fw), GFP_KERNEL);
+	fw = kzalloc(sizeof(*fw), GFP_KERNEL);
 	if (!fw)
 		return -ENOMEM;
 
@@ -247,6 +265,7 @@  static int rpi_firmware_probe(struct platform_device *pdev)
 	}
 
 	init_completion(&fw->c);
+	kref_init(&fw->consumers);
 
 	platform_set_drvdata(pdev, fw);
 
@@ -275,25 +294,35 @@  static int rpi_firmware_remove(struct platform_device *pdev)
 	rpi_hwmon = NULL;
 	platform_device_unregister(rpi_clk);
 	rpi_clk = NULL;
-	mbox_free_channel(fw->chan);
+
+	rpi_firmware_put(fw);
 
 	return 0;
 }
 
 /**
- * rpi_firmware_get - Get pointer to rpi_firmware structure.
  * @firmware_node:    Pointer to the firmware Device Tree node.
  *
+ * The reference to rpi_firmware has to be released with rpi_firmware_put().
+ *
  * Returns NULL is the firmware device is not ready.
  */
 struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
 {
 	struct platform_device *pdev = of_find_device_by_node(firmware_node);
+	struct rpi_firmware *fw;
 
 	if (!pdev)
 		return NULL;
 
-	return platform_get_drvdata(pdev);
+	fw = platform_get_drvdata(pdev);
+	if (!fw)
+		return NULL;
+
+	if (!kref_get_unless_zero(&fw->consumers))
+		return NULL;
+
+	return fw;
 }
 EXPORT_SYMBOL_GPL(rpi_firmware_get);
 
diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
index cc9cdbc66403..fdfef7fe40df 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -140,6 +140,7 @@  int rpi_firmware_property(struct rpi_firmware *fw,
 			  u32 tag, void *data, size_t len);
 int rpi_firmware_property_list(struct rpi_firmware *fw,
 			       void *data, size_t tag_size);
+void rpi_firmware_put(struct rpi_firmware *fw);
 struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
 #else
 static inline int rpi_firmware_property(struct rpi_firmware *fw, u32 tag,
@@ -154,6 +155,7 @@  static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
 	return -ENOSYS;
 }
 
+static inline void rpi_firmware_put(struct rpi_firmware *fw) { }
 static inline struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)
 {
 	return NULL;