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

Peter Zijlstra
2011-06-16T09:47:18Z

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.

Or I'm now confused, which isn't at all impossible with that code ;-)