Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check

From: Michal Hocko
Date: Wed Jun 01 2016 - 02:53:47 EST

On Wed 01-06-16 00:53:03, Oleg Nesterov wrote:
> On 05/31, Michal Hocko wrote:
> >
> > Oleg has pointed out that can simplify both oom_adj_write and
> > oom_score_adj_write even further and drop the sighand lock. The only
> > purpose of the lock was to protect p->signal from going away but this
> > will not happen since ea6d290ca34c ("signals: make task_struct->signal
> > immutable/refcountable").
> Sorry for confusion, I meant oom_adj_read() and oom_score_adj_read().
> As for oom_adj_write/oom_score_adj_write we can remove it too, but then
> we need to ensure (say, using cmpxchg) that unpriviliged user can not
> not decrease signal->oom_score_adj_min if its oom_score_adj_write()
> races with someone else (say, admin) which tries to increase the same
> oom_score_adj_min.

I am introducing oom_adj_mutex in a later patch so I will move it here.

> If you think this is not a problem - I am fine with this change. But
> please also update oom_adj_read/oom_score_adj_read ;)

will do. It stayed in the blind spot... Thanks for pointing that out

Michal Hocko