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SubjectRe: "Aiee: scheduling in interrupt 00111dd2" problem
How do I protect this 'race' from happening? I'm still not clear when to use: 
(1) save_flags(flags); cli(); ....critical code...... restore_flags(flags);
and when to use
(2) start_bh_atomic(); .....critical code....... end_bh_atomic();
Question: Can I use (2) when inside an interrupt handler? BTW, to Linux
what constitutes an interrupt handler? e.g. is do_dev_queue_xmit() an
interrupt handler?

thanks,
CCFoo

On Fri, 18 Dec 1998, Richard B. Johnson wrote:

> On Fri, 18 Dec 1998, Foo Chun Choong wrote:
>
> > Am I right to say that the locking structures are mainly used to prevent
> > race conditions. Why does the kernel hang when some of these are broken?
> >
>
> Observe a typical linked-list operation when the list in increasing in
> size (length) ....
>
> link = memory_from_somewhere();
> link->next = NULL;
>
> Now, look while it is decreasing in size...
>
> while(link != NULL) {
> save_next = link->next;
> memory_from_somewhere_free(link); /* (A) */
> link = save_next; /* (B) */
> }
>
> If another "thread" were to access ``link'' between A and B, it
> would be accessing invalid memory. If the first procedure was
> executing and didn't finish, before the next procedure was executed,
> all bets are off. This is a typical problem with multitasking, not
> just SMP. Some operations must complete before others are allowed.
>
> This if often called a "race" condition when, in fact it's no race
> at all, it's a "crash" condition, pure and simple.
>
>
> Cheers,
> Dick Johnson
> ***** FILE SYSTEM WAS MODIFIED *****
> Penguin : Linux version 2.1.131 on an i686 machine (400.59 BogoMips).
> Warning : It's hard to remain at the trailing edge of technology.
>
>


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