linux-kernel - Re: [BUG 4.9] New led trigger usbport gets the kernel to panic

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Date:   Fri, 2 Dec 2016 09:48:18 +0100
From:   Ralph Sennhauser <ralph.sennhauser@...il.com>
To:     Rafał Miłecki <rafal@...ecki.pl>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rafał Miłecki <zajec5@...il.com>
Subject: Re: [BUG 4.9] New led trigger usbport gets the kernel to panic

On Thu, 1 Dec 2016 17:56:07 +0100
Rafał Miłecki <rafal@...ecki.pl> wrote:

> On 12/01/2016 03:28 PM, Ralph Sennhauser wrote:
> > Below the oops with your debug patch applied.
> >
> > (...)
> >
> > root@...1900acs:/# cd sys/class/leds/pca963x\:shelby\:white\:usb2/
> > root@...1900acs:/sys/devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-0068/leds/pca963x:shelby:white:usb2#
> > echo usbport > trigger [  124.727665] leds
> > pca963x:shelby:white:usb2: [usbport_trig_add_port] port:dd708240
> > [  124.735266] leds pca963x:shelby:white:usb2:
> > [usbport_trig_add_port] port->port_name:usb1-port1
> > port->data:dd708140 [  124.745671] leds pca963x:shelby:white:usb2:
> > [usbport_trig_add_port] port:dd7083c0 [  124.753194] leds
> > pca963x:shelby:white:usb2: [usbport_trig_add_port]
> > port->port_name:usb2-port1 port->data:dd708140 [  124.763594] leds
> > pca963x:shelby:white:usb2: [usbport_trig_add_port] port:dd708300
> > [  124.771114] leds pca963x:shelby:white:usb2:
> > [usbport_trig_add_port] port->port_name:usb3-port1
> > port->data:dd708140
> > root@...1900acs:/sys/devices/platform/soc/soc:internal-regs/f1011000.i2c/i2c-0/0-0068/leds/pca963x:shelby:white:usb2#
> > echo 1 > ports/usb2-port1[  171.649751] leds
> > pca963x:shelby:white:usb2: [usbport_trig_port_store] buf:1
> > [  171.649751]  size:2
> >
> > [  171.660160] leds pca963x:shelby:white:usb2:
> > [usbport_trig_port_store] port:dd7083c0 [  171.668103] leds
> > pca963x:shelby:white:usb2: [usbport_trig_port_store]
> > port->port_name:usb2-port1 port->data:dd708140 [  171.678678]
> > [usbport_trig_update_count] usbport_data->count:0 [  171.684457]
> > [usbport_trig_update_count] usbport_data->count:0 [  171.690253]
> > Unable to handle kernel NULL pointer dereference at virtual address
> > 00000000  
> 
> Oh, so this happens a bit later than I expected or I could read from
> the backtrace. Anyway this debugging was still helpful, I think I can
> see a possible problem.
> 
> So most likely the crash happens at the:
> led_cdev->brightness_set(led_cdev, ...);
> call. I'm not sure what I was thinking when writing that code. It
> looks wrong.
> 
> The thing is some LEDs (drivers) don't provide brightness_set op.
> It's fine, we should just use brightness_set_blocking op when that
> happens. Of course kernel has proper helpers for that, we don't have
> to worry about the choice of op or scheduling the work. I have no
> idea why I didn't use a proper helper in the first place.
> 
> So we should simply replace above call with one of following ones:
> 1) led_set_brightness(led_cdev, ...);
> 2) led_set_brightness_nosleep(led_cdev, ...);
> 3) led_set_brightness_sync(led_cdev, ...);
> 
> I still have to check which one is correct. In theory we don't deal
> blinking at this point so we shouldn't need to use led_set_brightness.
> 
> led_set_brightness_nosleep looks like the most likely correct choice.
> 
> led_set_brightness_sync requires brightness_set_blocking which is not
> always present so most likely we don't want this one.
> 
> 
> If you have some free time and you want to play with this, please
> replace led_cdev->brightness_set
> with
> led_set_brightness_nosleep
> and give it a try. This should fix crashes for you.
> 
> I'll look at this again during next days.

Hi Rafał

I just gave 2) led_set_brightness_nosleep a try. The kernel no longer
crashes and the led does work as expected.

Thanks 
Ralph