linux-kernel - Re: Nokia N900: v4.16-rc4: oops in iio when grepping sysfs

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Date:   Sat, 10 Mar 2018 12:19:29 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
        jic23@...nel.org, akinobu.mita@...il.com, javier@....samsung.com,
        gregor.boirie@...rot.com
Cc:     pali.rohar@...il.com, sre@...nel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, khilman@...nel.org,
        aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
        patrikbachan@...il.com, serge@...lyn.com, abcloriens@...il.com,
        clayton@...ftyguy.net, martijn@...xit.nl,
        sakari.ailus@...ux.intel.com,
        Filip Matijević <filip.matijevic.pz@...il.com>,
        security@...nel.org, knaack.h@....de, pmeerw@...erw.net,
        linux-iio@...r.kernel.org
Subject: Re: Nokia N900: v4.16-rc4: oops in iio when grepping sysfs

On 03/10/2018 12:01 AM, Pavel Machek wrote:
[...]
>> What file are you opening to cause this?
> 
> Strace says:
> 
> openat(7, "in_intensity_both_thresh_rising_en",
>>> O_RDONLY|O_LARGEFILE|O_NOFOLLOW) = 3
> fstat64(3, {st_mode=S_IFREG|0644, st_size=4096, ...}) = 0
> ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbe83b714) = -1 ENOTTY
>>> (Inappropriate ioctl for device)
> read(3,
> Message from syslogd@...alhost at Mar  9 23:54:39 ...
>  kernel:[ 3097.357696] Internal error: Oops: 80000007 [#2] ARM
> 
> So that would be:
> 
> ./devices/platform/68000000.ocp/48072000.i2c/i2c-2/2-0029/iio:device1/events/in_intensity_both_thresh_rising_en
> 
> And indeed, manually cat-ing that file reproduces the problem.
> 
> pavel@...0:/sys/devices/platform/68000000.ocp/48072000.i2c/i2c-2/2-0029/iio:device1$
> cat name
> tsl2563
> 
> I can not find tsl2563 in MAINTAINERS, file is
> ./drivers/iio/light/tsl2563.c . I added few people pointed by git log.

The driver registers event attributes, but does not provide a handle to
access those attributes.

Now the question is how to best handle this case.

1) Return an error when the device is registered and abort registration
2) Skip registering the event attributes
3) Skip registering the event attributes, but print a warning
4) Register the attributes, but return an error when they are accessed

I'd prefer 2 since it offers a nice method of disabling all events for a
device (e.g. if not interrupt is provided).

On the other hand it could cause some confusion during development,
potentially causing the developer to wonder why he doesn't get any event
attributes even though he setup his channel description to have event
attributes.

Patch for 2.

--- a/drivers/iio/industrialio-event.c
+++ b/drivers/iio/industrialio-event.c
@@ -477,7 +477,8 @@ int iio_device_register_eventset(struct iio_dev
 	struct attribute **attr;

 	if (!(indio_dev->info->event_attrs ||
-	      iio_check_for_dynamic_events(indio_dev)))
+	      iio_check_for_dynamic_events(indio_dev)) ||
+	    !indio_dev->info->read_event_config)
 		return 0;

 	indio_dev->event_interface =