Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code

[Boris Ostrovsky]

On 06/12/2015 04:53 PM, Oleg Nesterov wrote:
> On 06/12, Oleg Nesterov wrote:
> > On 06/12, Ingo Molnar wrote:
> > > * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > > So I think the only issue is that ->mm can become NULL when the thread group
> > > > leader dies - a non-NULL mm should always be shared among all threads.
> > >
> > > Indeed, we do that in exit_mm().
> >
> > Yes,
> >
> > > So we could add tsk->mm_leader or so,
> >
> > No, no, please do not. Just do something like
> >
> > 	for_each_process(p) {
> >
> > 		for_each_thread(p, t) {
> > 			if (t->mm) {
> > 				do_something(t->mm);
> > 				break;
> > 			}
> > 		}
> > 	}
> >
> > But either way I don't understand what protects this ->mm. Perhaps this needs
> > find_lock_task_mm().
>
> And, I don't understand this code, probably this doesn't matter, but.
>
> unpin_all() is probably fine, but xen_mm_pin_all() can race with fork()
> and miss the new child. Is it OK?


Currently xen_mm_pin_all() is only called in the suspend path, out of 
stop_machine(), so presumably at that time fork is not possible.


-boris
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