Re: [PATCH] Tulip interrupt uses non IRQ safe spinlock

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

On Tue, May 03, 2005 at 09:25:26AM +0100, Mark Broadbent wrote:
>
> >> See Documentation/spin-locking.txt line 137, this states that
> >> spin_[un]lock() should not be used in IRQ handlers.
> 
> "If you have a case where you have to protect a data structure across
> several CPU's and you want to use spinlocks you can potentially use
> cheaper versions of the spinlocks. IFF you know that the spinlocks are
> never used in interrupt handlers, you can use the non-irq versions:
> 
>       spin_lock(&lock);
>       ...
>       spin_unlock(&lock);
> "

Yes this isn't very clear.

What it's trying to say that if you're in a softirq/user context
and the spin lock may be taken in an IRQ context elsewhere then
you must use the IRQ-disabling version.

However, if you're in the IRQ context yourself, and yours is the
only IRQ context that takes that spin lock, then you may use the
straight spin_lock version.

Cheers,
-- 
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