Re: [PATCH v4 3.0-rc2-tip 4/22] 4: Uprobes: register/unregister probes.

Srikar Dronamraju
2011-06-16T10:02:17Z

* Peter Zijlstra <peterz@infradead.org> [2011-06-16 11:46:22]:

> On Thu, 2011-06-16 at 09:41 +0530, Srikar Dronamraju wrote:
> > * Peter Zijlstra <peterz@infradead.org> [2011-06-15 19:41:59]:
> >
> > > On Tue, 2011-06-07 at 18:29 +0530, Srikar Dronamraju wrote:
> > > > 1. Use mm->owner and walk thro the thread_group of mm->owner, siblings
> > > > of mm->owner, siblings of parent of mm->owner. This should be
> > > > good list to traverse. Not sure if this is an exhaustive
> > > > enough list that all tasks that have a mm set to this mm_struct are
> > > > walked through.
> > >
> > > As per copy_process():
> > >
> > > /*
> > > * Thread groups must share signals as well, and detached threads
> > > * can only be started up within the thread group.
> > > */
> > > if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
> > > return ERR_PTR(-EINVAL);
> > >
> > > /*
> > > * Shared signal handlers imply shared VM. By way of the above,
> > > * thread groups also imply shared VM. Blocking this case allows
> > > * for various simplifications in other code.
> > > */
> > > if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
> > > return ERR_PTR(-EINVAL);
> > >
> > > CLONE_THREAD implies CLONE_VM, but not the other way around, we
> > > therefore would be able to CLONE_VM and not be part of the primary
> > > owner's thread group.
> > >
> > > This is of course all terribly sad..
> >
> > Agree,
> >
> > If clone(CLONE_VM) were to be done by a thread_group leader, we can walk
> > thro the siblings of parent of mm->owner.
> >
> > However if clone(CLONE_VM) were to be done by non thread_group_leader
> > thread, then we dont even seem to add it to the init_task. i.e I dont
> > think we can refer to such a thread even when we walk thro
> > do_each_thread(g,t) { .. } while_each_thread(g,t);
> >
> > right?
>
> No, we initialize p->group_leader = p; and only change that for
> CLONE_THREAD, so a clone without CLONE_THREAD always results in a new
> thread group leader, which are always added to the init_task list.
>

Ahh .. I missed the p->group_leader = p thing.

In which case, shouldnt traversing all the tasks of all siblings of
parent of mm->owner should provide us all the the tasks that have linked
to mm. Right?

Agree that we can bother about this a little later.

--
Thanks and Regards
Srikar