Re: [PATCH 3/7] em28xx: Only deallocate struct em28xx after finishing all extensions

["Frank Schäfer" <fschaefer.oss@googlemail.com>]

Am 13.01.2014 20:23, schrieb Mauro Carvalho Chehab:
> Em Mon, 13 Jan 2014 20:02:19 +0100
> Frank Schäfer <fschaefer.oss@googlemail.com> escreveu:
>
>> On 13.01.2014 00:00, Mauro Carvalho Chehab wrote:
>>> We can't free struct em28xx while one of the extensions is still
>>> using it.
>>>
>>> So, add a kref() to control it, freeing it only after the
>>> extensions fini calls.
>>>
>>> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
>>> ---
>>>   drivers/media/usb/em28xx/em28xx-audio.c |  5 ++++-
>>>   drivers/media/usb/em28xx/em28xx-cards.c | 34 ++++++++++++++++-----------------
>>>   drivers/media/usb/em28xx/em28xx-dvb.c   |  5 ++++-
>>>   drivers/media/usb/em28xx/em28xx-input.c |  8 +++++++-
>>>   drivers/media/usb/em28xx/em28xx-video.c | 11 +++++------
>>>   drivers/media/usb/em28xx/em28xx.h       |  9 +++++++--
>>>   6 files changed, 44 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/drivers/media/usb/em28xx/em28xx-audio.c b/drivers/media/usb/em28xx/em28xx-audio.c
>>> index 97d9105e6830..8e959dae8358 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-audio.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-audio.c
>>> @@ -878,6 +878,8 @@ static int em28xx_audio_init(struct em28xx *dev)
>>>   
>>>   	em28xx_info("Binding audio extension\n");
>>>   
>>> +	kref_get(&dev->ref);
>>> +
>>>   	printk(KERN_INFO "em28xx-audio.c: Copyright (C) 2006 Markus "
>>>   			 "Rechberger\n");
>>>   	printk(KERN_INFO
>>> @@ -949,7 +951,7 @@ static int em28xx_audio_fini(struct em28xx *dev)
>>>   	if (dev == NULL)
>>>   		return 0;
>>>   
>>> -	if (dev->has_alsa_audio != 1) {
>>> +	if (!dev->has_alsa_audio) {
>>>   		/* This device does not support the extension (in this case
>>>   		   the device is expecting the snd-usb-audio module or
>>>   		   doesn't have analog audio support at all) */
>>> @@ -963,6 +965,7 @@ static int em28xx_audio_fini(struct em28xx *dev)
>>>   		dev->adev.sndcard = NULL;
>>>   	}
>>>   
>>> +	kref_put(&dev->ref, em28xx_free_device);
>>>   	return 0;
>>>   }
>>>   
>>> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
>>> index 3b332d527ccb..df92f417634a 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-cards.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
>>> @@ -2867,16 +2867,18 @@ static void flush_request_modules(struct em28xx *dev)
>>>   	flush_work(&dev->request_module_wk);
>>>   }
>>>   
>>> -/*
>>> - * em28xx_release_resources()
>>> - * unregisters the v4l2,i2c and usb devices
>>> - * called when the device gets disconnected or at module unload
>>> -*/
>>> -void em28xx_release_resources(struct em28xx *dev)
>>> +/**
>>> + * em28xx_release_resources() -  unregisters the v4l2,i2c and usb devices
>>> + *
>>> + * @ref: struct kref for em28xx device
>>> + *
>>> + * This is called when all extensions and em28xx core unregisters a device
>>> + */
>>> +void em28xx_free_device(struct kref *ref)
>>>   {
>>> -	/*FIXME: I2C IR should be disconnected */
>>> +	struct em28xx *dev = kref_to_dev(ref);
>>>   
>>> -	mutex_lock(&dev->lock);
>>> +	em28xx_info("Freeing device\n");
>>>   
>>>   	if (dev->def_i2c_bus)
>>>   		em28xx_i2c_unregister(dev, 1);
>>> @@ -2887,9 +2889,10 @@ void em28xx_release_resources(struct em28xx *dev)
>>>   	/* Mark device as unused */
>>>   	clear_bit(dev->devno, &em28xx_devused);
>>>   
>>> -	mutex_unlock(&dev->lock);
>>> -};
>>> -EXPORT_SYMBOL_GPL(em28xx_release_resources);
>>> +	kfree(dev->alt_max_pkt_size_isoc);
>>> +	kfree(dev);
>>> +}
>>> +EXPORT_SYMBOL_GPL(em28xx_free_device);
>>>   
>>>   /*
>>>    * em28xx_init_dev()
>>> @@ -3342,6 +3345,8 @@ static int em28xx_usb_probe(struct usb_interface *interface,
>>>   			    dev->dvb_xfer_bulk ? "bulk" : "isoc");
>>>   	}
>>>   
>>> +	kref_init(&dev->ref);
>>> +
>>>   	request_modules(dev);
>>>   
>>>   	/* Should be the last thing to do, to avoid newer udev's to
>>> @@ -3390,12 +3395,7 @@ static void em28xx_usb_disconnect(struct usb_interface *interface)
>>>   
>>>   	em28xx_close_extension(dev);
>>>   
>>> -	em28xx_release_resources(dev);
>>> -
>>> -	if (!dev->users) {
>>> -		kfree(dev->alt_max_pkt_size_isoc);
>>> -		kfree(dev);
>>> -	}
>>> +	kref_put(&dev->ref, em28xx_free_device);
>>>   }
>>>   
>>>   static struct usb_driver em28xx_usb_driver = {
>>> diff --git a/drivers/media/usb/em28xx/em28xx-dvb.c b/drivers/media/usb/em28xx/em28xx-dvb.c
>>> index 5ea563e3f0e4..8674ae5fce06 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-dvb.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-dvb.c
>>> @@ -1010,11 +1010,11 @@ static int em28xx_dvb_init(struct em28xx *dev)
>>>   	em28xx_info("Binding DVB extension\n");
>>>   
>>>   	dvb = kzalloc(sizeof(struct em28xx_dvb), GFP_KERNEL);
>>> -
>>>   	if (dvb == NULL) {
>>>   		em28xx_info("em28xx_dvb: memory allocation failed\n");
>>>   		return -ENOMEM;
>>>   	}
>>> +	kref_get(&dev->ref);
>>>   	dev->dvb = dvb;
>>>   	dvb->fe[0] = dvb->fe[1] = NULL;
>>>   
>>> @@ -1442,6 +1442,7 @@ static int em28xx_dvb_init(struct em28xx *dev)
>>>   	dvb->adapter.mfe_shared = mfe_shared;
>>>   
>>>   	em28xx_info("DVB extension successfully initialized\n");
>>> +
>>>   ret:
>>>   	em28xx_set_mode(dev, EM28XX_SUSPEND);
>>>   	mutex_unlock(&dev->lock);
>>> @@ -1492,6 +1493,8 @@ static int em28xx_dvb_fini(struct em28xx *dev)
>>>   		dev->dvb = NULL;
>>>   	}
>>>   
>>> +	kref_put(&dev->ref, em28xx_free_device);
>>> +
>>>   	return 0;
>>>   }
>>>   
>>> diff --git a/drivers/media/usb/em28xx/em28xx-input.c b/drivers/media/usb/em28xx/em28xx-input.c
>>> index 61c061f3a476..33388b5922a0 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-input.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-input.c
>>> @@ -676,6 +676,8 @@ static int em28xx_ir_init(struct em28xx *dev)
>>>   		return 0;
>>>   	}
>>>   
>>> +	kref_get(&dev->ref);
>>> +
>>>   	if (dev->board.buttons)
>>>   		em28xx_init_buttons(dev);
>>>   
>>> @@ -814,7 +816,7 @@ static int em28xx_ir_fini(struct em28xx *dev)
>>>   
>>>   	/* skip detach on non attached boards */
>>>   	if (!ir)
>>> -		return 0;
>>> +		goto ref_put;
>>>   
>>>   	if (ir->rc)
>>>   		rc_unregister_device(ir->rc);
>>> @@ -822,6 +824,10 @@ static int em28xx_ir_fini(struct em28xx *dev)
>>>   	/* done */
>>>   	kfree(ir);
>>>   	dev->ir = NULL;
>>> +
>>> +ref_put:
>>> +	kref_put(&dev->ref, em28xx_free_device);
>>> +
>>>   	return 0;
>>>   }
>>>   
>>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
>>> index 587ff3fe9402..dc10cec772ba 100644
>>> --- a/drivers/media/usb/em28xx/em28xx-video.c
>>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
>>> @@ -1922,8 +1922,7 @@ static int em28xx_v4l2_fini(struct em28xx *dev)
>>>   	v4l2_ctrl_handler_free(&dev->ctrl_handler);
>>>   	v4l2_device_unregister(&dev->v4l2_dev);
>>>   
>>> -	if (dev->users)
>>> -		em28xx_warn("Device is open ! Memory deallocation is deferred on last close.\n");
>>> +	kref_put(&dev->ref, em28xx_free_device);
>>>   
>>>   	return 0;
>>>   }
>>> @@ -1945,11 +1944,9 @@ static int em28xx_v4l2_close(struct file *filp)
>>>   	mutex_lock(&dev->lock);
>>>   
>>>   	if (dev->users == 1) {
>>> -		/* free the remaining resources if device is disconnected */
>>> -		if (dev->disconnected) {
>>> -			kfree(dev->alt_max_pkt_size_isoc);
>>> +		/* No sense to try to write to the device */
>>> +		if (dev->disconnected)
>>>   			goto exit;
>>> -		}
>>>   
>>>   		/* Save some power by putting tuner to sleep */
>>>   		v4l2_device_call_all(&dev->v4l2_dev, 0, core, s_power, 0);
>>> @@ -2201,6 +2198,8 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>>>   
>>>   	em28xx_info("Registering V4L2 extension\n");
>>>   
>>> +	kref_get(&dev->ref);
>>> +
>>>   	mutex_lock(&dev->lock);
>>>   
>>>   	ret = v4l2_device_register(&dev->udev->dev, &dev->v4l2_dev);
>>> diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
>>> index 5d5d1b6f0294..d38c08e4da60 100644
>>> --- a/drivers/media/usb/em28xx/em28xx.h
>>> +++ b/drivers/media/usb/em28xx/em28xx.h
>>> @@ -32,6 +32,7 @@
>>>   #include <linux/workqueue.h>
>>>   #include <linux/i2c.h>
>>>   #include <linux/mutex.h>
>>> +#include <linux/kref.h>
>>>   #include <linux/videodev2.h>
>>>   
>>>   #include <media/videobuf2-vmalloc.h>
>>> @@ -531,9 +532,11 @@ struct em28xx_i2c_bus {
>>>   	enum em28xx_i2c_algo_type algo_type;
>>>   };
>>>   
>>> -
>>>   /* main device struct */
>>>   struct em28xx {
>>> +	struct kref ref;
>>> +
>>> +
>>>   	/* generic device properties */
>>>   	char name[30];		/* name (including minor) of the device */
>>>   	int model;		/* index in the device_data struct */
>>> @@ -706,6 +709,8 @@ struct em28xx {
>>>   	struct em28xx_dvb *dvb;
>>>   };
>>>   
>>> +#define kref_to_dev(d) container_of(d, struct em28xx, ref)
>>> +
>>>   struct em28xx_ops {
>>>   	struct list_head next;
>>>   	char *name;
>>> @@ -763,7 +768,7 @@ extern struct em28xx_board em28xx_boards[];
>>>   extern struct usb_device_id em28xx_id_table[];
>>>   int em28xx_tuner_callback(void *ptr, int component, int command, int arg);
>>>   void em28xx_setup_xc3028(struct em28xx *dev, struct xc2028_ctrl *ctl);
>>> -void em28xx_release_resources(struct em28xx *dev);
>>> +void em28xx_free_device(struct kref *ref);
>>>   
>>>   /* Provided by em28xx-camera.c */
>>>   int em28xx_detect_sensor(struct em28xx *dev);
>> I welcome this patch and the general approach looks good.
>> I had started working on the same issue, but it's not that trivial.
>>
>> At first glance there seem to be several issues, but I will need to 
>> review this patch in more detail and also make some tests.
>> Unfortunately, I don't have much time this evening, So could you please 
>> hold it back another day ?
>> I hope I can review the other remaining patch of this series (patch 5/7) 
>> later this evening.
> We're running out of time for 3.14. I think we should merge this patch
> series, and your patch series for 3.14, to be together with the em28xx-v4l
> split.
>
> My plan is to merge the remaining patches for 3.14 today or, in the worse
> case, tomorrow.
>
> If we slip on some bug, we'll still have the 3.14-rc cycle to fix, if the
> series gets merged, but, if we miss the bus, I'm afraid that we'll end
> by having more problems that will be hard to fix with trivial patches, due
> to em28xx-v4l split changes that also affected the driver removal and device
> close code.
>
> FYI, I tested this code and also Antti with our devices, randomly removing
> the devices while streaming, and this is now finally working.
>
> I won't doubt that there are some cases that require fixes (and
> it seems that em28xx-rc has one of such corner cases), but they'll likely
> can be solved with somewhat short and trivial patches.
>
> Cheers,
> Mauro

This is a very critical patch and exactly the kind of change that should
_never_ be hurried !
FAICS it has some severe issues and it's not clear how easy it will be
to fix it within the the 3.14-rc cycle.
As long as it's not ready, don't merge it for 3.14.

em28xx resources releasing is broken since ... well... at least 2 years.
3.14 will already be much better and nobody will care if this remaining
issue is addressed a kernel release later.

Be warned !