On Thu, 17 Nov 2011, Miao Xie wrote: > Oh~, David > > I find these is another problem, please take account of the following case: > > 2-3 -> 1-2 -> 0-1 > > the user change mems_allowed twice continuously, the task may see the empty > mems_allowed. > > So, it is still dangerous. > With this patch, we're protected by task_lock(tsk) to determine whether we want to take the exception, i.e. whether need_loop is false, and the setting of tsk->mems_allowed. So this would see the nodemask change at the individual steps from 2-3 -> 1-2 -> 0-1, not some inconsistent state in between or directly from 2-3 -> 0-1. The only time we don't hold task_lock(tsk) to change tsk->mems_allowed is when tsk == current and in that case we're not concerned about intermediate reads to its own nodemask while storing to a mask where MAX_NUMNODES > BITS_PER_LONG. Thus, there's no problem here with regard to such behavior if we exclude mempolicies, which this patch does. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>