On Fri, Nov 25, 2016 at 05:17:09PM +0100, Peter Zijlstra wrote: > On Fri, Nov 25, 2016 at 04:10:04PM +0000, Mark Rutland wrote: > > On Fri, Nov 25, 2016 at 04:21:39PM +0100, Dmitry Vyukov wrote: > > > > What are use cases for such primitive that won't be OK with "read once > > > _and_ atomically"? > > > > I have none to hand. > > Whatever triggers the __builtin_memcpy() paths, and even the size==8 > paths on 32bit. Lockref, per: http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02294.html In that specific case, a torn value just means we'll retry until we get a non torn value, due to the cmpxchg. For that case, all we need is the value to be reloaded per invocation of READ_ONCE(). This guy seems to have the full story: http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02389.html http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02558.html Thanks, Mark. -- 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
