linux-kernel - Re: [PATCH 4/4 v4] rtc: add rtc-driver for HID sensors of type time

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Date:	Fri, 14 Dec 2012 15:29:25 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	Jonathan Cameron <jic23@....ac.uk>, rtc-linux@...glegroups.com,
	Alessandro Zummo <a.zummo@...ertech.it>,
	srinivas pandruvada <srinivas.pandruvada@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/4 v4] rtc: add rtc-driver for HID sensors of type time

Am 14.12.2012 15:15, schrieb Alexander Holler:
> Am 14.12.2012 14:08, schrieb Alexander Holler:
>> Am 14.12.2012 10:42, schrieb Lars-Peter Clausen:
>
>>> And another thing I've overlooked before:
>>> wait_for_completion_interruptible_timeout can either return a positive
>>> number when the completion was completed, 0 in case of an timeout, or a
>>> negative error code in case it was interrupted. You need to handle all
>>> three. E.g. something like this.
>>>
>>> ret = wait_for_completion_interruptible_timeout(...)
>>> if (ret == 0)
>>>     return -EIO;
>>> if (ret < 0)
>>>     return ret
>>>
>>
>> Hmpf, the only working approach to use some in kernel functions really
>> is to the read source yourself and don't trust anything else. :/
>
> Anyway, my approach doesn't work as it introduces a race condition:
>
>
> /* get a report with all values through requesting one value */
> sensor_hub_input_attr_get_raw_value(...)
>
> /* race if this task goes to slepp and the values were
> received before it could call the below wait...
>
> /* wait for all values (event) */
> if (!wait_for_completion_interruptible_timeout(...))
>
>
> I'll have to look for a mechanism how to avoid that. So v5 might need
> some time.

Sorry for the noise. That INIT_COMPLETION() before the sensor...() does 
exactly that. So it's enough if I handle the different return situations 
of wait_for...().

I will just use if(wait...()<=0) return -EIO.

Regards,

Alexander
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