Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

2020-11-23 Thread Nicolas Saenz Julienne 
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
> >  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(>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



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Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

2020-11-12 Thread Dmitry Torokhov 
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
>  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(>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.

-- 
Dmitry
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Re: [PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

2020-11-12 Thread Andy Shevchenko 
On Thu, Nov 12, 2020 at 6:40 PM Nicolas Saenz Julienne
 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(>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;
>  }


-- 
With Best Regards,
Andy Shevchenko
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[PATCH v4 01/11] firmware: raspberrypi: Keep count of all consumers

2020-11-12 Thread Nicolas Saenz Julienne 
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 
Signed-off-by: Nicolas Saenz Julienne 
---

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(-)

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 
+#include 
 #include 
 #include 
 #include 
@@ -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(>consumers, rpi_firmware_delete);
+}
+EXPORT_SYMBOL_GPL(rpi_firmware_put);
+
 static int rpi_firmware_probe(struct platform_device *pdev)
 {
struct device *dev = >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(>c);
+   kref_init(>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(>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;
-- 
2.29.2

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