Hi Tejun,

On 10/22, Tejun Heo wrote:

On Mon, Oct 22, 2012 at 07:44:04PM +0200, Oleg Nesterov wrote:

quoted

We probably have another similar race. If ptrace_stop()->may_ptrace_stop()
returns false, the task does

	__set_current_state(TASK_RUNNING);
	// no mb in between
	try_to_freeze();

And this can race with task_is_stopped_or_traced() check in the same way.
(of course this is only theoretical).

do_signal_stop() is probably fine, we can rely on ->siglock.

Hmm....  Guess we should drop __ from set_current_state.

Yes.

Or we can change ptrace_stop() and do_signal_stop() to use freezer_do_not_count/
freezer_count and remove task_is_stopped_or_traced() from update_if_frozen()
and try_to_freeze_tasks(). But this means that do_signal_stop() will call
try_to_freeze() twice, unless we add __freezer_count() which only clears
PF_FREEZER_SKIP.

I wonder
whether we should just add mb to freezing()?  What do you think?

Yes, I thought about this too. I just do not know what would be better.

Oleg.