Messages in this thread Patch in this message | | | From | Libin <> | Subject | [PATCH 01/14] kthread: Fix invalid wakeup in kthreadd | Date | Thu, 29 Aug 2013 21:57:36 +0800 |
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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 <huawei.libin@huawei.com> --- 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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