LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Lars-Peter Clausen <firstname.lastname@example.org>
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Dmitry Torokhov <email@example.com>
Cc: Eugen Hristev <firstname.lastname@example.org>,
Jonathan Cameron <email@example.com>,
Subject: Re: [PATCH v3 06/11] iio: inkern: add module put/get on iio dev module when requesting channels
Date: Wed, 18 Apr 2018 14:37:01 +0200 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 04/18/2018 11:35 AM, Jonathan Cameron wrote:
> On Tue, 17 Apr 2018 12:19:06 -0700
> Dmitry Torokhov <email@example.com> wrote:
>> Hi Eugen,
>> On Tue, Apr 17, 2018 at 10:39:24AM +0300, Eugen Hristev wrote:
>>> On 17.04.2018 02:58, Dmitry Torokhov wrote:
>>>> On Sun, Apr 15, 2018 at 08:33:21PM +0100, Jonathan Cameron wrote:
>>>>> On Tue, 10 Apr 2018 11:57:52 +0300
>>>>> Eugen Hristev <firstname.lastname@example.org> wrote:
>>>>>> When requesting channels for a particular consumer device,
>>>>>> besides requesting the device (incrementing the reference counter), also
>>>>>> do it for the driver module of the iio dev. This will avoid the situation
>>>>>> where the producer IIO device can be removed and the consumer is still
>>>>>> present in the kernel.
>>>>>> Signed-off-by: Eugen Hristev <email@example.com>
>>>>>> drivers/iio/inkern.c | 8 +++++++-
>>>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
>>>>>> index ec98790..68d9b87 100644
>>>>>> --- a/drivers/iio/inkern.c
>>>>>> +++ b/drivers/iio/inkern.c
>>>>>> @@ -11,6 +11,7 @@
>>>>>> #include <linux/slab.h>
>>>>>> #include <linux/mutex.h>
>>>>>> #include <linux/of.h>
>>>>>> +#include <linux/module.h>
>>>>>> #include <linux/iio/iio.h>
>>>>>> #include "iio_core.h"
>>>>>> @@ -152,6 +153,7 @@ static int __of_iio_channel_get(struct iio_channel *channel,
>>>>>> if (index < 0)
>>>>>> goto err_put;
>>>>>> channel->channel = &indio_dev->channels[index];
>>>>>> + try_module_get(channel->indio_dev->driver_module);
>>>>> And if it fails? (the module we are trying to get is going away...)
>>>>> We should try and handle it I think. Be it by just erroring out of here.
>>>> Even more, this has nothing to do with modules. A device can go away for
>>>> any number of reasons (we unbind it manually via sysfs, we pull the USB
>>>> plug from the host in case it is USB-connected device, we unload I2C
>>>> adapter for the bus device resides on, we kick underlying PCI device)
>>>> and we should be able to handle this in some fashion. Handling errors
>>>> from reads and ignoring garbage is one of methods.
>>>> FWIW this is a NACK from me.
>>> This patch is actually a "best effort attempt" for the consumer driver
>>> (touch driver) to get a reference to the producer of the data (the IIO
>>> device), when it requests the specific channels.
>>> As of this moment, there is no attempt whatsoever for the consumer to have a
>>> reference on the producer driver. Thus, the producer can be removed at any
>>> time, and the consumer will fail ungraciously.
>> This is the root of the issue. The consumer should be prepared to handle
>> errors from producer.
>>> I can change the perspective from "best effort" to "mandatory" to get a
>>> reference to the producer, or you wish to stop trying to get any reference
>>> at all (remove this patch completely) ?
>> You should take reference to the device itself (if it is not taken
>> already), so it does not disappear completely and you can continue using
>> IIO API to access it, and IIO API should be prepared to deal with "dead"
>> devices, but as I pointed in my other email, trying to pin the driver
>> is quite pointless as there are myriad other ways of device stopping
>> working besides module unloading.
>> In any case, I think this problem is outside of the scope of this
>> patchset that adds a generic resistive touchscreen, so if you want to
>> continue working on this I'd recommend moving it into a separate series.
> Agreed, this one has come up a number of times before. Quite a lot of
> work got done by (IIRC) Lars Peter Clausen to stabilize things in various
> unexpected 'going away' events. Of course there may be paths we have
> added since that (it was years ago) that can cause trouble...
> Anyhow, separate issue as Dmitry says, let's deal with it separately.
We do properly get a ref to the device. Not getting a ref to the module is
on purpose. Cause as Dmitry said it does nothing the device can disappear at
any point either way. I second the NACK.
next prev parent reply other threads:[~2018-04-18 12:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-10 8:57 [PATCH v3 00/11] Add support for SAMA5D2 touchscreen Eugen Hristev
2018-04-10 8:57 ` [PATCH v3 01/11] iio: adc: at91-sama5d2_adc: fix channel configuration for differential channels Eugen Hristev
2018-04-15 19:23 ` Jonathan Cameron
2018-04-10 8:57 ` [PATCH v3 02/11] MAINTAINERS: add generic resistive touchscreen adc Eugen Hristev
2018-04-10 8:57 ` [PATCH v3 03/11] iio: Add channel for Position Relative Eugen Hristev
2018-04-15 19:29 ` Jonathan Cameron
2018-04-17 7:30 ` Eugen Hristev
2018-04-18 9:32 ` Jonathan Cameron
2018-04-10 8:57 ` [PATCH v3 04/11] dt-bindings: input: touchscreen: add pressure threshold touchscreen property Eugen Hristev
2018-04-13 18:33 ` Rob Herring
2018-04-10 8:57 ` [PATCH v3 05/11] dt-bindings: input: touchscreen: resistive-adc-touch: create bindings Eugen Hristev
2018-04-13 18:34 ` Rob Herring
2018-04-10 8:57 ` [PATCH v3 06/11] iio: inkern: add module put/get on iio dev module when requesting channels Eugen Hristev
2018-04-15 19:33 ` Jonathan Cameron
2018-04-16 23:58 ` Dmitry Torokhov
2018-04-17 7:39 ` Eugen Hristev
2018-04-17 19:19 ` Dmitry Torokhov
2018-04-18 9:35 ` Jonathan Cameron
2018-04-18 12:37 ` Lars-Peter Clausen [this message]
2018-04-10 8:57 ` [PATCH v3 07/11] iio: adc: at91-sama5d2_adc: add support for position and pressure channels Eugen Hristev
2018-04-15 19:45 ` Jonathan Cameron
2018-04-10 8:57 ` [PATCH v3 08/11] input: touchscreen: resistive-adc-touch: add generic resistive ADC touchscreen Eugen Hristev
2018-04-23 23:22 ` Dmitry Torokhov
2018-04-23 23:24 ` Dmitry Torokhov
2018-04-10 8:57 ` [PATCH v3 09/11] dt-bindings: iio: adc: at91-sama5d2_adc: add channel specific consumer info Eugen Hristev
2018-04-10 8:57 ` [PATCH v3 10/11] ARM: dts: at91: sama5d2: add channel cells for ADC device Eugen Hristev
2018-04-10 8:57 ` [PATCH v3 11/11] ARM: dts: at91: sama5d2: Add resistive touch device Eugen Hristev
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--subject='Re: [PATCH v3 06/11] iio: inkern: add module put/get on iio dev module when requesting channels' \
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).