Re: [PATCH v3] EM28xx - fix deadlock when unplugging and replugging a DVB adapter

[Chris Rankin]

On 25/09/11 14:00, Mauro Carvalho Chehab wrote:
Hmm... This would probably work better (not tested). Could you please test it
on your hardware?

Hmm, I don't understand this. The deadlock isn't about taking 
em28xx_devlist_mutex, but happens because em28xx_dvb_init() tries to retake 
dev->lock when em28xx_usb_probe() is already holding it. That's why I unlocked 
dev->lock before calling em28xx_init_extension().

So why are you avoiding locking em28xx_devlist_mutex?

Cheers,
Chris

diff --git a/drivers/media/video/em28xx/em28xx-cards.c 
b/drivers/media/video/em28xx/em28xx-cards.c
index 7297d90..c92c177 100644
--- a/drivers/media/video/em28xx/em28xx-cards.c
+++ b/drivers/media/video/em28xx/em28xx-cards.c
@@ -3005,7 +3005,8 @@ static int em28xx_init_dev(struct em28xx **devhandle, 
struct usb_device *udev,
                goto fail;
        }

-       em28xx_init_extension(dev);
+       /* dev->lock needs to be holded */
+       __em28xx_init_extension(dev);

        /* Save some power by putting tuner to sleep */
        v4l2_device_call_all(&dev->v4l2_dev, 0, core, s_power, 0);
@@ -3301,10 +3302,10 @@ static void em28xx_usb_disconnect(struct usb_interface 
*interface)
                em28xx_release_resources(dev);
        }

-       em28xx_close_extension(dev);
-
        mutex_unlock(&dev->lock);

+       em28xx_close_extension(dev);
+
        if (!dev->users) {
                kfree(dev->alt_max_pkt_size);
                kfree(dev);
diff --git a/drivers/media/video/em28xx/em28xx-core.c 
b/drivers/media/video/em28xx/em28xx-core.c
index 804a4ab..afddfea 100644
--- a/drivers/media/video/em28xx/em28xx-core.c
+++ b/drivers/media/video/em28xx/em28xx-core.c
@@ -1218,16 +1218,22 @@ void em28xx_unregister_extension(struct em28xx_ops *ops)
  }
  EXPORT_SYMBOL(em28xx_unregister_extension);

-void em28xx_init_extension(struct em28xx *dev)
+/* Need to take the mutex lock before calling it */
+void __em28xx_init_extension(struct em28xx *dev)
  {
        const struct em28xx_ops *ops = NULL;

-       mutex_lock(&em28xx_devlist_mutex);
        list_add_tail(&dev->devlist,&em28xx_devlist);
        list_for_each_entry(ops,&em28xx_extension_devlist, next) {
                if (ops->init)
                        ops->init(dev);
        }
+}
+
+void em28xx_init_extension(struct em28xx *dev)
+{
+       mutex_lock(&em28xx_devlist_mutex);
+       __em28xx_init_extension(dev);
        mutex_unlock(&em28xx_devlist_mutex);
  }

diff --git a/drivers/media/video/em28xx/em28xx.h 
b/drivers/media/video/em28xx/em28xx.h
index 1626e4a..a5c1ba2 100644
--- a/drivers/media/video/em28xx/em28xx.h
+++ b/drivers/media/video/em28xx/em28xx.h
@@ -682,6 +682,7 @@ void em28xx_remove_from_devlist(struct em28xx *dev);
  void em28xx_add_into_devlist(struct em28xx *dev);
  int em28xx_register_extension(struct em28xx_ops *dev);
  void em28xx_unregister_extension(struct em28xx_ops *dev);
+void __em28xx_init_extension(struct em28xx *dev);
  void em28xx_init_extension(struct em28xx *dev);
  void em28xx_close_extension(struct em28xx *dev);


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