Re: [RFC,PATCH 2/2] cputimers/proc:do_task_stat()->thread_group_times() is racy and O(n) under->siglock

[Stanislaw Gruszka]

On Thu, Mar 25, 2010 at 01:12:50PM +0100, Oleg Nesterov wrote:
> > but more importantly I think
> > clock_gettime(CLOCK_PROCESS_CPUTIME_ID) should indeed use ->siglock to
> > ensure it serializes against do_exit() so that either we iterate the
> > thread or get the accumulated runtime from signal_struct but not both
> > (or neither).
> 
> Oh. I forgot everything I knew about posix-cpu-timers... But, it seems,
> posix_cpu_clock_get() calls thread_group_cputime() under tasklist and
> thus can't race with exit.

We assure thread_group_cputime() is called with one of: tasklist_lock
or ->siglock to avoid races with __exit_signal. Except oom killer and
elf core-dump code where is no lock, where we assume exit is not called
or we don't care of inaccurate results.

Stanislaw
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/