On Fri, Oct 09, 2015 at 12:21:55PM +0000, Kosuke Tatsukawa wrote: > + * Memory barrier is required here to make sure change to > + * vcpu->async_pf.done is visible from other CPUs. This memory > + * barrier pairs with prepare_to_wait's set_current_state() That is not how memory barriers work; they don't 'make visible'. They simply ensure order between operations. X = Y = 0 CPU0 CPU1 [S] X=1 [S] Y=1 MB MB [L] y=Y [L] x=X assert(x || y) The issue of the memory barrier does not mean the store is visible, it merely means that the load _must_ happen after the store (in the above scenario). This gives a guarantee that not both x and y can be 0. Because either being 0, means the other has not yet executed and must therefore observe your store. Nothing more, nothing less. So your comment is misleading at best. -- 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
