On Sat, Mar 9, 2013 at 12:01 PM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > threadgroup_lock() takes signal->cred_guard_mutex to ensure that > thread_group_leader() is stable. This doesn't look nice, the scope > of this lock in do_execve() is huge. > > And as Dave pointed out this can lead to deadlock, we have the > following dependencies: > > do_execve: cred_guard_mutex -> i_mutex > cgroup_mount: i_mutex -> cgroup_mutex > attach_task_by_pid: cgroup_mutex -> cred_guard_mutex > > Change de_thread() to take threadgroup_change_begin() around the > switch-the-leader code and change threadgroup_lock() to avoid > ->cred_guard_mutex. > > Note that de_thread() can't sleep with ->group_rwsem held, this > can obviously deadlock with the exiting leader if the writer is > active, so it does threadgroup_change_end() before schedule(). > > Reported-by: Dave Jones <davej@xxxxxxxxxx> > Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
