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On Tue, 24 Jul 2007, Benjamin Herrenschmidt wrote: > > In fact, it's more than that... the bitops that return a value are often > used to have hand-made spinlock semantics. I'm sure we would get funky > bugs if loads or stores leaked out of the locked region. I think a full > "memory" clobber should be kept around for those cases. Not helpful. The CPU ordering constraints for "test_and_set_bit()" and friends are weak enough that even if you have a full memory clobber, it still wouldn't work as a lock. That's exactly why we have smp_mb__after_set_bit() and friends. On some architectures (arm, mips, parsic, powerpc), *that* is where the CPU memory barrier is, because the "test_and_set_bit()" itself is just a cache-coherent operation, not an actual barrier. Linus - 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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