Re: [PATCH v3] mm, oom: Fix race when selecting process to kill

[Sameer Nanda <snanda@chromium.org>]

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On Sat, Nov 9, 2013 at 7:16 AM, Oleg Nesterov <oleg@redhat.com> wrote:

> On 11/08, Sameer Nanda wrote:
> >
> > @@ -413,12 +413,20 @@ void oom_kill_process(struct task_struct *p, gfp_t
> gfp_mask, int order,
> >                                             DEFAULT_RATELIMIT_BURST);
> > @@ -456,10 +463,18 @@ void oom_kill_process(struct task_struct *p, gfp_t
> gfp_mask, int order,
> >                       }
> >               }
> >       } while_each_thread(p, t);
> > -     read_unlock(&tasklist_lock);
> >
> >       rcu_read_lock();
> > +
> >       p = find_lock_task_mm(victim);
> > +
> > +     /*
> > +      * Since while_each_thread is currently not RCU safe, this unlock
> of
> > +      * tasklist_lock may need to be moved further down if any
> additional
> > +      * while_each_thread loops get added to this function.
> > +      */
> > +     read_unlock(&tasklist_lock);
>
> Well, ack... but with this change find_lock_task_mm() relies on tasklist,
> so it makes sense to move rcu_read_lock() down before for_each_process().
> Otherwise this looks confusing, but I won't insist.
>

Agreed that this looks a bit confusing.  I will respin the patch.


>
> Oleg.
>
>


-- 
Sameer

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