Re: [PATCH v2] Document /proc/pid PID reuse behavior

Michal Hocko
2018-11-07T16:00:19Z

On Wed 07-11-18 15:48:20, Daniel Colascione wrote:
> On Tue, Nov 6, 2018 at 1:05 PM, Michal Hocko <mhocko@kernel.org> wrote:
> > On Mon 05-11-18 13:22:05, Daniel Colascione wrote:
> >> State explicitly that holding a /proc/pid file descriptor open does
> >> not reserve the PID. Also note that in the event of PID reuse, these
> >> open file descriptors refer to the old, now-dead process, and not the
> >> new one that happens to be named the same numeric PID.
> >
> > This sounds quite obvious
>
> Many people *on* *LKML* were wrong about this behavior. If it's not
> obvious to experienced kernel developers, it's certainly not obvious
> to the public.

Fair enough

> > otherwise anybody could simply DoS the system
> > by consuming all available pids.
>
> People can do that today using the instrument of terror widely known
> as fork(2). The only thing standing between fork(2) and a full process
> table is RLIMIT_NPROC.

not really. If you really do care about pid space depletion then you
should use pid cgroup controller.
--
Michal Hocko
SUSE Labs