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On Mon, 6 Nov 2006, Benjamin Herrenschmidt wrote: > > > Yes. On x86 (and x86-64) you'll never see this, because writes are always > > seen in order regardless, and in addition, the spin_lock is actually > > totally serializing anyway. On most other architectures, the spin_lock > > will serialize all the writes too, but it's not guaranteed, so in theory > > you're right. I suspect no actual architecture will do this, but hey, > > when talking memory ordering, safe is a lot better than sorry. > > PowerPC doesn't serialize the writes on spin_lock, only on spin_unlock. > > (That is, previous writes can "leak" into the lock, but writes done > before the unlock can't leak out of the spinlock). > > Now, I've just glanced at the thread, so I don't know if that's relevant > to the problems you guys are talking about :-) > It is relevant. In powerpc, can one write happen before another write? x = 1; barrier(); (only compiler barrier) b = 2; And have CPU 2 see b=2 before seeing x=1? If so, then I guess this is indeed a bug on powerpc. -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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