Daniel Walker wrote:
On Tue, 2006-04-25 at 20:11 +1000, Nick Piggin wrote:
I guess it is so it can be used in NMIs and interrupts without turning
interrupts off (so is somewhat lightweight).
But please Daniel, just use spinlocks and trylock. This is buggy because
it doesn't get the required release consistency correct.
To use spinlock we would need to used the __raw_ types . As Hua
explained all of the vanilla spinlock calls use the unlikely macro. The
result is that we end up using atomic operations. So using them directly
seems like the cleanest method .
Ah, I see. Then you should be OK with either your current scheme, or
Andrew's suggestion, so long as you have a memory barrier before the
unlock (eg. smp_mb__before_clear_bit()).
I'm not exactly sure what you mean by "release consistency" ?
Without a barrier, the stores to the linked list may be visible to another
CPU after the store that unlocks the atomic_t. Ie. the critical section can
leak out of the lock.
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