Re: [rfc][patch] Avoid taking global tasklist_lock for single threadedprocess at getrusage()

[Oleg Nesterov <oleg@tv-sign.ru>]

Christoph Lameter wrote:
> 
> On Sat, 24 Dec 2005, Oleg Nesterov wrote:
> 
> > I can't understand this. 'p' can do clone(CLONE_THREAD) immediately
> > after 'if (!thread_group_empty(p))' check.
> 
> Only if p != current. As discussed later the lockless approach is
> intened to only be used if p == current.

Unless I missed something this function (getrusage_both) is called
from wait_noreap_copyout,

> +++ linux-2.6.15-rc6/kernel/exit.c	2005-12-23 10:42:16.000000000 -0800
> @@ -38,7 +38,7 @@
>  extern void sem_exit (void);
>  extern struct task_struct *child_reaper;
>  
> -int getrusage(struct task_struct *, int, struct rusage __user *);
> +int getrusage_both(struct task_struct *, struct rusage __user *);
>  
>  static void exit_mm(struct task_struct * tsk);
>  
> @@ -994,7 +994,7 @@
>  			       struct siginfo __user *infop,
>  			       struct rusage __user *rusagep)
>  {
> -	int retval = rusagep ? getrusage(p, RUSAGE_BOTH, rusagep) : 0;
> +	int retval = rusagep ? getrusage_both(p, rusagep) : 0;
>  	put_task_struct(p);

(the diff lacks '-p' parameter)

So p != current.

Oleg.
-
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