From: Dmitry Adamushko <[EMAIL PROTECTED]>
Subject: kthread: call wake_up_process() whithout the lock being held
- from the POV of synchronization, there should be no need to call
wake_up_process()
with the 'kthread_create_lock' being held;
- moreover, in order to support a lockless check for
list_empty(&kthread_create_list)
in kthreadd() :
set_current_state(TASK_INTERRUPTIBLE);
if (list_empty(&kthread_create_list))
schedule();
we must ensure that a modification of the list (i.e. list_add_tail()) has been
completed
by the moment a state of the task is checked in try_to_wake_up().
i.e. they must not be re-ordered.
wake_up_process() (i.e. try_to_wake_up() effectively) doesn't provide a full mb.
By moving wake_up_process() out of the locked section, we get an UNLOCK/LOCK
pair (LOCK is in try_to_wake_up()) which is guaranteed to act as a full mb.
Signed-off-by: Dmitry Adamushko <[EMAIL PROTECTED]>
diff --git a/kernel/kthread.c b/kernel/kthread.c
index d7a7897..ec68e0f 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -158,9 +158,9 @@ struct task_struct *kthread_create(int (*threadfn)(void
*data),
spin_lock(&kthread_create_lock);
list_add_tail(&create.list, &kthread_create_list);
- wake_up_process(kthreadd_task);
spin_unlock(&kthread_create_lock);
+ wake_up_process(kthreadd_task);
wait_for_completion(&create.done);
if (!IS_ERR(create.result)) {
--
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