Re: [PATCH] 2.4.18 raid1 - fix SMP locking/interrupt

Manfred Spraul (
Mon, 25 Mar 2002 20:50:26 +0100

> 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
e.g. if it calls kmalloc(GFP_KERNEL), down(), schedule(), etc.


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