>> 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.
How about a less dangerous variant thereof...
Q> while (link != NULL) {
Q> save := link;
Q> link := link->next;
Q> memory_from_somewhere_free(save);
Q> }
That should be thread-safe since link never points anywhere invalid...
> This if often called a "race" condition when, in fact it's no race
> at all, it's a "crash" condition, pure and simple.
To be accurate, it's a bug, pure and simple...
Best wishes from Riley.
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