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SubjectRe: [PATCH] i386 spinlocks should use the full 32 bits, not only 8 bits


On Fri, 21 Oct 2005, Ingo Molnar wrote:
>
> the unlock is simple even in the preemption case

No it's not. It needs to decrement the preemption counter and test it.

See kernel/spinlock.c:

void __lockfunc _spin_unlock(spinlock_t *lock)
{
_raw_spin_unlock(lock);
preempt_enable();
}
EXPORT_SYMBOL(_spin_unlock);
and look at what "preempt_enable()" does.

In other words, with CONFIG_PREEMPT, your patch is WRONG. You made
"spin_unlock()" just skip the preempt_enable.

In fact, with preemption, the _locking_ is the simpler part. Unlock is the
complex one.


Linus
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