Oleg Nesterov <[email protected]> writes:
> A lot of kernel threads parented to /sbin/init slow down do_wait() when
> a non-detached (user-space) process exits. Change reparent_kthread() to
> use init_task as a parent. Since init_task can't go away, we don't need
> to put the caller on init_task.children list.
Is there any downside of putting tasks on init_task.children?
If not it is probably a good idea to put processes there just for good measure.
> NOTE: pstree doesn't show kernel threads with this patch.
>
> Signed-off-by: Oleg Nesterov <[email protected]>
>
> --- 2.6.21-rc5/kernel/exit.c~3_SWAPPER 2007-04-10 21:59:41.000000000 +0400
> +++ 2.6.21-rc5/kernel/exit.c 2007-04-10 22:25:25.000000000 +0400
> @@ -255,11 +255,11 @@ static int has_stopped_jobs(struct pid *
> }
>
> /**
> - * reparent_kthread - Reparent the calling kernel thread to the init task of
> the pid space that the thread belongs to.
> + * reparent_kthread - Reparent the calling kernel thread to swapper.
> *
> * If a kernel thread is launched as a result of a system call, or if
> - * it ever exits, it should generally reparent itself to init so that
> - * it is correctly cleaned up on exit.
> + * it ever exits, it should generally reparent itself so that it is
> + * correctly cleaned up on exit.
> *
> * The various task state such as scheduling policy and priority may have
> * been inherited from a user process, so we reset them to sane values here.
> @@ -272,9 +272,8 @@ void reparent_kthread(void)
>
> ptrace_unlink(current);
> remove_parent(current);
> - current->parent = init_pid_ns.child_reaper;
> + current->parent = &init_task;
> current->real_parent = current->parent;
> - add_parent(current);
>
> /* make the task auto-reap */
> current->exit_signal = -1;
-
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