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    SubjectRe: [PATCH] 2.4.18 raid1 - fix SMP locking/interrupt
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    >
    > However a bare spin_unlock_irq() in a function means that
    > callers which wish to keep interrupts disabled are subtly
    > subverted. We've had bugs from this before.
    >
    It is trivial to catch such bugs at runtime. I tried it a year ago, and
    immediately run into sleep_on() users that legitimately call
    spin_lock_irq() with disabled interrupts. Perhaps they are gone now,
    I'll retest my patch.

    > So the irqrestore functions are much more robust. I believe
    > that they should be the default choice. The non-restore
    > versions should be viewed as a micro-optimised version,
    > to be used with caution. The additional expense of the save/restore
    > is quite tiny - 20-30 cycles, perhaps.

    OTHO, if a function doesn't work correctly if it's called with disabled
    interrupts, then it should not use spin_lock_irqsave() - it's
    misleading.
    e.g. if it calls kmalloc(GFP_KERNEL), down(), schedule(), etc.

    --
    Manfred

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