Re: [PATCH 1/7] mm: remove cgroup_mm_owner_callbacks

[Hugh Dickins <hugh@veritas.com>]

On Wed, 19 Nov 2008, Paul Menage wrote:
> On Wed, Nov 19, 2008 at 5:11 PM, Hugh Dickins <hugh@veritas.com> wrote:
> >
> >  assign_new_owner:
> >        BUG_ON(c == p);
> >        get_task_struct(c);
> > -       read_unlock(&tasklist_lock);
> > -       down_write(&mm->mmap_sem);
> >        /*
> >         * The task_lock protects c->mm from changing.
> >         * We always want mm->owner->mm == mm
> >         */
> >        task_lock(c);
> > +       /*
> > +        * Delay read_unlock() till we have the task_lock()
> > +        * to ensure that c does not slip away underneath us
> > +        */
> > +       read_unlock(&tasklist_lock);
> 
> How can c slip away when we've done get_task_struct(c) earlier?

I don't know, I did vaguely wonder the same myself: just putting
this back to how it was before (including that comment),
maybe Balbir can enlighten us.

Hugh

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