On 04/18/2018 11:35 AM, Jonathan Cameron wrote: > On Tue, 17 Apr 2018 12:19:06 -0700 > Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> 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 <eugen.hristev@xxxxxxxxxxxxx> 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 <eugen.hristev@xxxxxxxxxxxxx> >>>>>> --- >>>>>> 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. >>>> >>>> Thanks. >>> Hello, >>> >>> 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. >> >> Thanks. >> > 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. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
