Messages in this thread Patch in this message | | | Date | Mon, 16 Jan 2012 20:51:40 +0900 | From | Yasunori Goto <> | Subject | Re: [BUG] TASK_DEAD task is able to be woken up in special condition |
| |
> Ok. Thansk for your agreement. > I'll test this patch.
Hi.
I tested this patch. I've not found any problems so far. Please merge it.
----- try_to_wake_up() has a problem which may change status from TASK_DEAD to TASK_RUNNING in race condition with SMI or guest environment of virtual machine. (See: https://lkml.org/lkml/2011/12/21/523) As a result, exited task is scheduled() again and panic occurs.
By this patch, do_exit() waits for releasing task->pi_lock which is used in try_to_wake_up(). It guarantees the task becomes TASK_DEAD after waking up.
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
--- kernel/exit.c | 8 ++++++++ 1 file changed, 8 insertions(+)
Index: linux-3.2/kernel/exit.c =================================================================== --- linux-3.2.orig/kernel/exit.c +++ linux-3.2/kernel/exit.c @@ -1038,6 +1038,14 @@ NORET_TYPE void do_exit(long code) preempt_disable(); exit_rcu(); + + /* + * try_to_wake_up() might be waking me up due to race condition. + * Make sure it is finished. + */ + 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
| |