Re: [PATCH] pid: improved namespaced iteration over processes list

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

Gowrishankar M <gomuthuk-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org> writes:

> Below patch addresses a common solution for any place where a process
> should be checked if it is associated to caller namespace. At present,
> we use 'task_pid_vnr(t) > 0' to further proceed with task 't' in current
> namespace.
>
> To avoid applying this check in every code related to PID namespace,
> this patch reworks on iterative macros;for_each_process and do_each_thread.

Which is just wrong.  Most of the time when we call for_each_process
and do_each_thread we are iterating through them for kernel internal purposes
not because of a user space request.

> This patch can also reduce latency time on process list lookup inside the
> container, as we walk along pidmap, instead of every process in system.

I support walking pidmap, in those cases where it makes sense.  kill -1
in particular.

But I don't think there are any significant unconverted instances of
that problem.

So specific helpers to do the job is fine (if the problem is more general
than kill -1) but changing the generic helpers looks like a good way
to introduce lots of subtle bugs into the kernel.  So different names
please.

Eric