to schedule() or not to schedule() ?

Kevin Diggs kevdig at
Wed Aug 6 05:26:35 EST 2008

Chris Friesen wrote:
> Kevin Diggs wrote:
>> Hi,
>>     I have the following near the top of my cpufreq driver target 
>> routine:
>> while(test_and_set_bit(cf750gxmCfgChangeBit,&cf750gxvStateBits)) {
>>         /*
>>          * Someone mucking with our cfg? (I hope it is ok to call
>>          * schedule() here! - truth is I have no idea what I am doing
>>          * ... my reasoning is I want to yeild the cpu so whoever is
>>          * mucking around can finish)
>>          */
>>         schedule();
>> }
>> This is to prevent bad things from happening if someone is trying to 
>> change a parameter for the driver via sysfs while the target routine 
>> is running. Fortunately, because I had a bug where this bit was not 
>> getting cleared on one of the paths through the target routine ... I 
>> now know it is not safe to call schedule (it got stuck in there - 
>> knocked out my adb keyboard! - (I think target is called from a timer 
>> that the governor sets up ... interrupt context?)).
> Is the issue that someone may be in the middle of a multi-stage 
> procedure, and you've woken up partway through?
> If so, what about simply rescheduling the timer for some short time in 
> the future and aborting the current call?
> Chris


	Thanks for taking the time to reply. The parameter in question modifies 
the frequency table. It is used several times in the target routine. 
I've addressed the issue by making a local copy of the frequency table 
upon entry to the target routine and use that while there. I don't care 
who wins the race.


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