On 11/10, Oleg Nesterov wrote: > > And the 3rd case which I didn't think about yesterday. And now I really hope > it can explain the vmcore we have. > > If sysctl_sched_autogroup_enabled was enabled and then disabled, it is > possible that the "autogrouped" process runs with ag->kref.refcount == 1, > and if it does setsid() it frees its active task_group.
And yet another problem ;) The exiting thread must call sched_move_task() somewhere before exit_notify() or it can run with the freed task_group() after that. And this means that the no-longer-needed PF_EXITING check in task_wants_autogroup() will be needed again. Simple, but needs the comments/changelog... > So I am going to send the patch which simply moves the sysctl check from > autogroup_move_group() to sched_autogroup_create_attach(), but perhaps I > should split this change? > > I mean, the first patch for -stable could just remove the current check, > the 2nd one will add it into sched_autogroup_create_attach(). No, this is not enough, see above. I am starting to think that we should just move ->autogroup from signal_struct to task_struct. This will simplify the code and fix all these problems. But I need a simple fix for backporting anyway. Oleg.
