On Thu, 23 Nov 2006 10:47:55 +0100
Sébastien Dugué <[email protected]> wrote:
> On Thu, 23 Nov 2006 00:40:53 -0800
> Andrew Morton <[email protected]> wrote:
>
> > On Thu, 23 Nov 2006 09:28:05 +0100
> > Sébastien Dugué <[email protected]> wrote:
> >
> > > > > + target = good_sigevent(&event);
> > > > > +
> > > > > + if (unlikely(!target || (target->flags & PF_EXITING)))
> > > > > + goto out_unlock;
> > > > > +
> > > > > +
> > > > > +
> > > > > + if (notify->notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
> > > > > + /*
> > > > > + * This reference will be dropped in really_put_req() when
> > > > > + * we're done with the request.
> > > > > + */
> > > > > + get_task_struct(target);
> > > > > + }
> > > >
> > > > It worries me that this function can save away a task_struct* without
> > > > having taken a reference against it.
> > > >
> > >
> > > OK. Does moving 'notify->target = target;' after the get_task_struct() will
> > > do, or am I missing something more subtle?
> >
> > Well it's your code - you tell me ;)
> >
> > It is unsafe (and rather pointless) to be saving the address of some structure
> > which can be freed at any time.
>
> Sorry, I expressed myself quite badly. What I wanted to know is whether you
> are worried with the task been freed between saving its pointer and getting a
> ref on it (which is trivial to fix) or you are thinking of something deeper.
>
Look:
> + notify->target = target;
> +
> + if (notify->notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
> + /*
> + * This reference will be dropped in really_put_req() when
> + * we're done with the request.
> + */
> + get_task_struct(target);
If that test fails, we've saved a pointer to the task_struct without having
taken a refreence on it.
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