On Fri, Nov 25, 2016 at 04:21:39PM +0100, Dmitry Vyukov wrote: > > READ/WRITE_ONCE imply atomicity. Even if their names don't spell it (a > function name doesn't have to spell all of its guarantees). Most of > the uses of READ/WRITE_ONCE will be broken if they are not atomic. In practice, this is certainly the assumption made by many/most users of the *_ONCE() accessors. Looking again, Linus does seem to agree that word-sized accesses should result in single instructions (and be single-copy atomic) [1], so in contrast to [2], that's clearly *part* of the point of the *_ONCE() accessors... > "Read once but not necessary atomically" is a very subtle primitive > which is very easy to misuse. I agree. Unfortunately, Linus does not appear to [2]. > What are use cases for such primitive that won't be OK with "read once > _and_ atomically"? I have none to hand. Thanks, Mark. [1] http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02674.html [2] http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02670.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
