The patch titled
kthread: call wake_up_process() without the lock being held
has been added to the -mm tree. Its filename is
kthread-call-wake_up_process-without-the-lock-being-held.patch
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------------------------------------------------------
Subject: kthread: call wake_up_process() without the lock being held
From: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
- 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 <dmitry.adamushko@xxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Andy Whitcroft <apw@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kthread.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/kthread.c~kthread-call-wake_up_process-without-the-lock-being-held kernel/kthread.c
--- a/kernel/kthread.c~kthread-call-wake_up_process-without-the-lock-being-held
+++ a/kernel/kthread.c
@@ -158,9 +158,9 @@ struct task_struct *kthread_create(int (
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)) {
_
Patches currently in -mm which might be from dmitry.adamushko@xxxxxxxxx are
kthread-synchronization-issues.patch
kthread-add-a-missing-memory-barrier-to-kthread_stop.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
-
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