Re: preemptive kernel

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On Thu, 2003-09-11 at 23:50, kkonaka@mac.com wrote:
> howdy,
> 
> suppose I have a (character) driver code,
> 
> does the following piece of code break under preemptive
> kernel option enabled?  -- is there any pointer regarding
> precisely when kernel preemption can take place?
> 
> TIA
> kenji
> 
> --
> int busy = 0;
> wait_queue_head_t q;
> some_resource res; /* data structure shared between processes */
> 
> ssize_t my_write(struct file * file, const char * buf,
>                        size_t count, loff_t *ppos)
> {
>     while (busy) {    /* grab exclusive access */
>       interruptible_sleep_on(&q);  
>     }
> 
>     <do something assuming exclusive access to resources>
> 
>     busy = 0;        /* release exclusive access */
>     wake_up_interruptible(&q);
>     return retval;


this code already breaks even without a non-preemptible kernel.....
your use of *_sleep_on() is defective.

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