Andrew Morton wrote: > On Wed, 16 Apr 2008 21:17:34 -0700 "Paul Menage" <menage@xxxxxxxxxx> wrote: > >> On Wed, Apr 16, 2008 at 9:11 PM, Andrew Morton >> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >>> I don't fully understand the race. Both paths hold css_set_lock. >>> >>> Can you describe it in more detail please? >> Task A starts exiting, passes the check for unlinking current->cg_list. > > So cgroup_exit() sees !list_empty(tsk->cg_list) > cgroup_exit() sees list_empty(tsk->cg_list), then cgroup_enable_task_cg_list() links the task to the list, and then the task exited, so the list entry won't get deleted. > And the list_del() sets tsk->cg_list to LIST_POISON[12], which still means > !list_empty(). Or we remove that debugging code and avoid writing to > tsk->cg_list, and it _still_ is !list_empty(). > >> Before it completely exits task B does the very first >> cgroup_iter_begin() call (via reading a cgroups tasks file) which >> links all tasks in to their css_set objects via tsk->cg_list. > > But it won't link this task, because it's !list_empty(). > >> Then task A finishes exiting and is freed, but doesn't unlink from the cg_list. >> >>> afacit the task at *p could set PF_EXITING immediately after this code has >>> tested PF_EXITING and then the task at *p could proceed until we hit the >>> same race (whatever that is). >> The important fact there is that the task sets PF_EXITING *before* it >> checks whether it needs to unlink from current->cg_list. >> >> Paul > > _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
