Re: [patch 4/4] taskstats: Export "cdata_acct" with taskstats

[Oleg Nesterov <oleg@redhat.com>]

On 11/25, Michael Holzheu wrote:
>
> Hello Oleg,
>
> On Thu, 2010-11-25 at 14:26 +0100, Oleg Nesterov wrote:
> > On 11/19, Michael Holzheu wrote:
> > >
> > > From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
> > >
> > > With this patch the (full) cumulative CPU time is added to "struct taskstats".
> > > The CPU time is only returned for the thread group leader.
> > >
> > > ...
> > >
> > > +	if (tsk->tgid == tsk->pid
> >
> > thread_group_leader() ?
>
> Yes, that's better.
>
> > > && lock_task_sighand(tsk, &flags)) {
> >
> > Do you really need ->siglock? Starting from 2.6.35 it is always
> > safe to access ->signal.
>
> Hmmm, if you say that...
>
> I just did it like it is done in e.g. fs/proc/base.c (proc_pid_limits).
> Can we remove the locking there, too?

We can certainly remove more siglock's which were previously
needed to access ->signal.

This particular one is just wrong. We need task_lock(group_leader)
to read signal->rlim atomically. However, it is not trivial to do
this correctly. Probably we should ignore this minor problem.

In any case, this ->siglock buys nothing today.

Oleg.