Re: [RFC 5/7] mm: introduce external memory hinting API

[Michal Hocko]

On Tue 28-05-19 08:33:06, Minchan Kim wrote:
> On Mon, May 27, 2019 at 05:12:02PM +0200, Oleg Nesterov wrote:
> > On 05/27, Minchan Kim wrote:
> > >
> > > > another problem is that pid_task(pid) can return a zombie leader, in this case
> > > > mm_access() will fail while it shouldn't.
> > >
> > > I'm sorry. I didn't notice that. However, I couldn't understand your point.
> > > Why do you think mm_access shouldn't fail even though pid_task returns
> > > a zombie leader?
> > 
> > The leader can exit (call sys_exit(), not sys_exit_group()), this won't affect
> > other threads. In this case the process is still alive even if the leader thread
> > is zombie. That is why we have find_lock_task_mm().
> 
> Thanks for clarification, Oleg. Then, Let me have a further question.
> 
> It means process_vm_readv, move_pages have same problem too because find_task_by_vpid
> can return a zomebie leader and next line checks for mm_struct validation makes a
> failure. My understand is correct? If so, we need to fix all places.

Isn't that a problem of most callers of get_task_mm? Shouldn't we fix it
turning it into find_lock_task_mm?
-- 
Michal Hocko
SUSE Labs