On Mon, 9 Jun 2014, Gu Zheng wrote: > > I think your patch addresses the problem that you're reporting but misses > > the larger problem with cpuset.mems rebinding on fork(). When the > > forker's task_struct is duplicated (which includes ->mems_allowed) and it > > races with an update to cpuset_being_rebound in update_tasks_nodemask() > > then the task's mems_allowed doesn't get updated. > > Yes, you are right, this patch just wants to address the bug reported above. > The race condition you mentioned above inherently exists there, but it is yet > another issue, the rcu lock here makes no sense to it, and I think we need > additional sync-mechanisms if want to fix it. Yes, the rcu lock is not providing protection for any critical section here that requires (1) the forker's cpuset to be stored in cpuset_being_rebound or (2) the forked thread's cpuset to be rebound by the cpuset nodemask update, and no race involving the two. > But thinking more, though the current implementation has flaw, but I worry > about the negative effect if we really want to fix it. Or maybe the fear > is unnecessary.:) > It needs to be slightly rewritten to work properly without negatively impacting the latency of fork(). Do you have the cycles to do it? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>