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

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Message-ID: <50CB347B.80305@ahsoftware.de>
Date:	Fri, 14 Dec 2012 15:15:23 +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 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.


Regards,

Alexander

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