Hi David, On 06/09/2014 05:13 PM, David Rientjes wrote: > 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 be honest, I'm busy with other schedule. And if you(or other guys) have proper proposal, please go ahead. To Tejun, Li and Andrew: Any comment? Or could you apply this *bug fix* first? Regards, Gu -- 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>