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 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
