On Thu 29-09-11 18:37:24, Oleg Nesterov wrote:

On 09/29, Michal Hocko wrote:

quoted

On Thu 29-09-11 14:05:17, Oleg Nesterov wrote:

quoted

But of course this can't help if freeze_task() is called later.
May be freezable() should check TIF_MEMDIE...

Wouldn't it be easier to ignore try_to_freeze when fatal signals are
pending in get_signal_to_deliver?

Oh, I don't think so. For what? This doesn't close other races, and
in fact the fatal_signal_pending() this patch adds is itself racy,
SIGKILL can come in between.

OK, I think I see your point. You mean that oom will send KILL after
both fatal_signal_pending in refrigerator and signal_pending check in
schedule, right?

quoted

--- a/kernel/freezer.c
+++ b/kernel/freezer.c

@@ -48,6 +48,11 @@ void refrigerator(void)
 	current->flags |= PF_FREEZING;

 	for (;;) {
+		if (fatal_signal_pending(current)) {
+			if (freezing(current) || frozen(current))
+				thaw_process(current);

Ah, I didn't mean refrigerator() should check freezing/frozen.

I meant, oom_kill can do this before thaw thaw_process(), afaics
this should fix the particular race you described (but not others).

This is what the follow up fix from David is doing. Check frozen in
select_bad_process if the task is TIF_MEMDIE and thaw the process.

And it seems that the David's follow up fix is sufficient so let's leave
refrigerator alone.
Or am I still missing something?

And. It is simply wrong to return from refrigerator() after we set
PF_FROZEN, this can fool try_to_freeze_tasks(). Sure, thaw_process()
from oom_kill is not nice too, but at least this is the special case,
we already have the problem.

Oleg.

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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
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Czech Republic

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