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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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