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

[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?

Oleg.