Re: [BUG] TASK_DEAD task is able to be woken up in special condition

Yasunori Goto
2012-01-06T12:01:26Z

> On Fri, 2012-01-06 at 19:22 +0900, Yasunori Goto wrote:
> > I just confirmed booting up on my box, and I would like to get rough agreement
> > about this way to solve this issue at first.
>
> I really don't like it. It makes the ttwu path more complex and more
> expensive. ttwu is one of the hottest and more complex paths in the
> scheduler, it needs neither more overhead nor more complexity.

Hmmmmm.
Ok.
>
> I'd really much rather put another raw_spin_unlocked_wait() in do_exit()
> before we set TASK_DEAD. It probably needs an smp memory barrier too.

Do you mean the following patch?

---

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>

---
kernel/exit.c | 4 ++++
1 file changed, 4 insertions(+)

Index: linux-3.2-rc7/kernel/exit.c
===================================================================
--- linux-3.2-rc7.orig/kernel/exit.c
+++ linux-3.2-rc7/kernel/exit.c
@@ -1038,6 +1038,10 @@ NORET_TYPE void do_exit(long code)

preempt_disable();
exit_rcu();
+
+ smp_mb();
+ raw_spin_unlock_wait(&tsk->pi_lock);
+
/* causes final put_task_struct in finish_task_switch(). */
tsk->state = TASK_DEAD;
schedule();

--
Yasunori Goto