Hello Oleg,
On Tue, 2010-11-23 at 17:59 +0100, Oleg Nesterov wrote:
> On 11/19, Michael Holzheu wrote:
> > TODO:
> > -----
> > With this patch we take the siglock twice. First for the dead task
> > and second for the parent of the dead task. This give the following
> > lockdep warning (probably a lockdep annotation is needed here):
>
> And we already discussed this ;) We do not need 2 siglock's, only
> parent's. Just move the callsite in __exit_signal() down, under
> another (lockless) group_dead check.
>
> Or I missed something?
The problem with moving this down to the second group_dead check is that
after __unhash_process() is called, pid_alive(tsk) which is checked in
thread_group_cputime() returns false. Therefore we always get zero CPU
times.
So I probably have to introduce a second group_dead check at the
beginning of __exit_signal():
@@ -150,6 +153,9 @@ static void __exit_signal(struct task_st
struct sighand_struct *sighand;
struct tty_struct *uninitialized_var(tty);
+ if (group_dead)
+ __account_cdata(...);
+
sighand = rcu_dereference_check(tsk->sighand,
rcu_read_lock_held() ||
> We can do this before taking ->siglock. Not that I think this really
> matters, but otherwise this looks a bit confusing imho, as if we need
> parent's ->siglock to pin something.
ok
>
>
> And thanks for splitting these changes. It was much, much easier to
> read now.
My personal feeling is that probably the only acceptable thing would be
to make the new behavior configurable with a sysctl and define the
default as it currently is (POSIX compliant).
This would only introduce two additional checks in __exit_signal() and
wait_task_zombie() and would not add any new fields to the
signal_struct.
Michael
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