If kthreadd is preempted at(or before) location a, and the other thread,
such as calling kthread_create_on_node(), adds a list item to
the kthread_create_list followed with wake_up_process(kthread). After that
when kthreadd is re-scheduled, calling set_current_state to set itself as
state TASK_INTERRUPTIBLE, if it is preempted again after that and before
__set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem.
------------------------
kthreadd()
------------------------
...
for (;;) {
//location a
set_current_state(TASK_INTERRUPTIBLE);
if (list_empty(&kthread_create_list)) {
//location b
schedule();
//location c
}
__set_current_state(TASK_RUNNING);
//location d
...
------------------------
kthread_create_on_node()
------------------------
...
spin_lock(&kthread_create_lock);
list_add_tail(&create.list, &kthread_create_list);
spin_unlock(&kthread_create_lock);
...
wake_up_process(kthreadd_task);
...
To solve this problem, using preempt_disable() to bound the operaion that
setting the task state and the conditions(set by the wake thread) validation.
------------------------
kthreadd()
------------------------
...
for (;;) {
preempt_disable();
set_current_state(TASK_INTERRUPTIBLE);
if (list_empty(&kthread_create_list)) {
preempt_enable();
schedule();
preempt_disable();
}
...
Signed-off-by: Libin <[email protected]>
---
kernel/kthread.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 760e86d..25c3fed 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -456,10 +456,15 @@ int kthreadd(void *unused)
current->flags |= PF_NOFREEZE;
for (;;) {
+ preempt_disable();
set_current_state(TASK_INTERRUPTIBLE);
- if (list_empty(&kthread_create_list))
+ if (list_empty(&kthread_create_list)) {
+ preempt_enable();
schedule();
+ preempt_disable();
+ }
__set_current_state(TASK_RUNNING);
+ preempt_enable();
spin_lock(&kthread_create_lock);
while (!list_empty(&kthread_create_list)) {
--
1.8.2.1
--
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