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

From: Michal Hocko
Date: Tue May 31 2016 - 03:32:37 EST

On Mon 30-05-16 19:43:24, Oleg Nesterov wrote:
> On 05/30, Michal Hocko wrote:
> >
> > both oom_adj_write and oom_score_adj_write are using task_lock,
> > check for task->mm and fail if it is NULL. This is not needed because
> > the oom_score_adj is per signal struct so we do not need mm at all.
> > The code has been introduced by 3d5992d2ac7d ("oom: add per-mm oom
> > disable count") but we do not do per-mm oom disable since c9f01245b6a7
> > ("oom: remove oom_disable_count").
> >
> > The task->mm check is even not correct because the current thread might
> > have exited but the thread group might be still alive - e.g. thread
> > group leader would lead that echo $VAL > /proc/pid/oom_score_adj would
> > always fail with EINVAL while /proc/pid/task/$other_tid/oom_score_adj
> > would succeed. This is unexpected at best.
> >
> > Remove the lock along with the check to fix the unexpected behavior
> > and also because there is not real need for the lock in the first place.


> and we should also remove lock_task_sighand(). as for oom_adj_read() and
> oom_score_adj_read() we can just remove it right now; it was previously
> needed to ensure the task->signal != NULL, today this is always true.

OK, I will add the following patch to the series.