Re: [PATCH] namespaces: fix race at task exit

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Oleg Nesterov (oleg@tv-sign.ru):
> On 01/25, Serge E. Hallyn wrote:
> >
> > In do_exit(), the exit_task_namespaces() was placed after
> > exit_notify() because exit_notify ends up using the pid
> > namespace both to access the reaper, and for detaching the
> > pid.  However, this placement allows an nfs server to reap
> > the task before exit_task_namespaces() completes.
> > 
> > This patch moves the exit_task_namespaces() into release_task,
> > below release_thread() which puts the pids(), and just above
> > the call_rcu(delayed_put_task_struct).  I believe this should
> > solve both problems.
> > 
> > Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
> > 
> > ---
> > 
> >  kernel/exit.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > 765277a4170d7bbd1c4613de661ec6ac64d5580a
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index 3540172..ab9ae30 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -174,6 +174,7 @@ repeat:
> >  	write_unlock_irq(&tasklist_lock);
> >  	proc_flush_task(p);
> >  	release_thread(p);
> > +	exit_task_namespaces(p);
> >  	call_rcu(&p->rcu, delayed_put_task_struct);
> 
> Probably I missed some other patches in this area, but I can't understand
> this fix.
> 
> With this change we are doing __put_mnt_ns() when we surely don't have ->sighand,
> no? Could you please explain?

Explanation: it's wrong  :)

we'll just need to break exit_task_namespaces() up.

thanks,
-serge
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