From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out-011.synserver.de ([212.40.185.11]:1184 "EHLO smtp-out-011.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756224Ab2LNQdC (ORCPT ); Fri, 14 Dec 2012 11:33:02 -0500 Message-ID: <50CB54C3.1090409@metafoo.de> Date: Fri, 14 Dec 2012 17:33:07 +0100 From: Lars-Peter Clausen MIME-Version: 1.0 To: Alexander Holler CC: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, Jonathan Cameron , rtc-linux@googlegroups.com, Alessandro Zummo , srinivas pandruvada , Andrew Morton Subject: Re: [PATCH 4/4 v4] rtc: add rtc-driver for HID sensors of type time References: <50C8591A.3030301@ahsoftware.de> <1355310680-2466-1-git-send-email-holler@ahsoftware.de> <50CAF473.6040901@metafoo.de> <50CB24D4.3030606@ahsoftware.de> <50CB347B.80305@ahsoftware.de> <50CB37C5.4050008@ahsoftware.de> <50CB38F2.4050806@metafoo.de> <50CB44B3.8040601@ahsoftware.de> In-Reply-To: <50CB44B3.8040601@ahsoftware.de> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 12/14/2012 04:24 PM, Alexander Holler wrote: > Am 14.12.2012 15:34, schrieb Lars-Peter Clausen: >> On 12/14/2012 03:29 PM, Alexander Holler wrote: >>> 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. >>> >> >> No, that's wrong. You should really return the error code returned by >> wait_for_completion_interruptible_timeout(). This will make sure that >> userspace restarts the syscall if necessary. > > Sorry for my ignorance, but which reasons for interruption do exist > which doesn't kill the userspace too? The error number -ESYSRESTART > doesn't offer a hint. Well I'm not an expert on this either, but as far as I know any signal the process is listening on can cause an interruption. Most signals won't kill the process though. More on the whole restart stuff: http://lwn.net/Articles/528935/ - Lars