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Nick Piggin <nickpiggin@yahoo.com.au> wrote: > Shouldn't be needed: Documentation/atomic_ops.txt specifies that any atomic_ > which both modifies its atomic operand and returns something is to be a full > barrier before and after the operation. Hmmm... It's possible that I've misunderstood what atomic_ops.txt actually says. For instance: | int atomic_inc_and_test(atomic_t *v); | int atomic_dec_and_test(atomic_t *v); | | These two routines increment and decrement by 1, respectively, the | given atomic counter. They return a boolean indicating whether the | resulting counter value was zero or not. | | It requires explicit memory barrier semantics around the operation as | above. Note the last paragraph. "It requires" should be "They require", but the sense would seem to be obvious. However, it's not clear on a second reading as to whether this is an instruction to the _caller_ or an instruction to the arch _implementer_. I suppose from reading the abstract at the top: | This document is intended to serve as a guide to Linux port maintainers on | how to implement atomic counter, bitops, and spinlock interfaces properly. that it is meant to be read by the implementor and not the user/caller, in which case, Nick is correct. It seems I need to adjust my memory barrier doc, and perhaps I should adjust atomic_ops.txt too to make it clearer. David - 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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