linux-kernel - Re: [PATCH] media: dvb_frontend: dvb_unregister_frontend must not call dvb

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Date:   Sun, 26 Nov 2017 18:10:42 +0100
From:   Daniel Scheller <d.scheller.oss@...il.com>
To:     Wolfgang Rohdewald <wolfgang@...dewald.de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: dvb_frontend: dvb_unregister_frontend must not
 call dvb_detach for fe->ops.release

Am Fri, 24 Nov 2017 15:02:30 +0100
schrieb Wolfgang Rohdewald <wolfgang@...dewald.de>:

> because ops.release was never dvb_attached.
> Which makes sense because f->ops.release does not attach anything.
> 
> Now, rmmod dvb_usb_pctv452e correctly sets counters for
> stb6100/stb0899 to 0.
> 
> Before, stb0899 got a counter -1, and for my 4 receivers I got 3
> OOPses like
> 
> Nov 24 14:40:41 s5 kernel: [  194.211014] WARNING: CPU: 6 PID: 3055 at
>    module_put.part.45+0x132/0x1a0
> Call Trace:
>  ? _stb0899_read_reg+0x100/0x100 [stb0899]
>  ? _stb0899_read_reg+0x100/0x100 [stb0899]
>  symbol_put_addr+0x38/0x60
>  dvb_frontend_put+0x42/0x60 [dvb_core]
>  ? stb0899_sleep+0x50/0x50 [stb0899]
>  dvb_frontend_detach+0x7c/0x90 [dvb_core]
>  dvb_usb_adapter_frontend_exit+0x57/0x80 [dvb_usb]
>  dvb_usb_exit+0x39/0xb0 [dvb_usb]
>  dvb_usb_device_exit+0x3f/0x60 [dvb_usb]
>  pctv452e_usb_disconnect+0x6f/0x80 [dvb_usb_pctv452e]
>  usb_unbind_interface+0x75/0x290
>  ? _raw_spin_unlock_irqrestore+0x4a/0x80
>  device_release_driver_internal+0x160/0x210
>  driver_detach+0x40/0x80
>  bus_remove_driver+0x5c/0xd0
>  driver_unregister+0x2c/0x40
>  usb_deregister+0x6c/0xf0
>  pctv452e_usb_driver_exit+0x10/0xec0 [dvb_usb_pctv452e]
> 
> Signed-off-by: Wolfgang Rohdewald <wolfgang@...dewald.de>
> ---
>  drivers/media/dvb-core/dvb_frontend.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/dvb-core/dvb_frontend.c
> b/drivers/media/dvb-core/dvb_frontend.c index
> 9139d01ba7ed..c2cc794299c9 100644 ---
> a/drivers/media/dvb-core/dvb_frontend.c +++
> b/drivers/media/dvb-core/dvb_frontend.c @@ -150,7 +150,8 @@ static
> void __dvb_frontend_free(struct dvb_frontend *fe) 
>  	dvb_free_device(fepriv->dvbdev);
>  
> -	dvb_frontend_invoke_release(fe, fe->ops.release);
> +	if (fe->ops.release)
> +		fe->ops.release(fe);
>  
>  	kfree(fepriv);
>  	fe->frontend_priv = NULL;

FWIW, this patch breaks unloading for all DVB cards in my dev system,
in that attached drivers like demod and tuner drivers won't usecount
to zero anymore ("rmmod ddbridge" keeps the usecount of stv0367 and
cxd2841er up, and "rmmod budget_av" doesn't usecount the tda10023 back
to zero).

Best regards,
Daniel Scheller
-- 
https://github.com/herrnst