Re: spin_lock() around sleepable function?

["Peter Teoh" <htmldeveloper@xxxxxxxxx>]

On 3/18/08, Arvin Moezzi <moezzia@xxxxxxxxx> wrote:
> On 3/17/08, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
>  > Looking at schedule_work() below:
>  >
>  >  fs/file.c:
>  >
>  >                fddef = &get_cpu_var(fdtable_defer_list);
>  >                 spin_lock(&fddef->lock);
>  >                 fdt->next = fddef->next;
>  >                 fddef->next = fdt;
>  >                 /* vmallocs are handled from the workqueue context */
>  >                 schedule_work(&fddef->wq);===>
>  >                 spin_unlock(&fddef->lock);
>  >
>  >  can schedule_work() sleep?   if so, then holding a spin_lock (which is
>  >  supposed to be used for quick turnaround operation) across a sleepable
>  >  functions look risky here (though it is possible to design this way,
>  >  but the classic CPU 100% bug is possible - sleep and never wake up,
>  >  resulting in another CPU going into spin_lock mode - churning up 100%
>  >  CPU time).   Or may be I am wrong?
>  >
>  >  Can calling this function schedule_work() ever ended the entire task
>  >  being reassigned to another CPU?   If so, then, will it not defeats
>  >  the purpose of using the per_cpu function get_cpu_var()?
>  >
>  >  How about schedule() -->ever ended the entire task being reassigned to
>  >  another CPU? ?
>  >
>
>
> Hey Peter,
>
>  btw. have you found out whether or not a "spin_lock" after "get_cpu_var"
>  makes sense. I couldn't understand it either.
>
>
>  Arvin
>

Discussion thread is here:

http://www.gossamer-threads.com/lists/linux/kernel/892870?do=post_view_flat#892870

I am still replying his email.......trying to understand these....

-- 
Regards,
Peter Teoh

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