On 09/01, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> > Yes, this should work. But I _think_ we can make the better fix...
> >
> > I'll try to make the patch soon. Afaics we don't need
> > kthreadd_task_init_done.
>
> ok.
Just in case, the patch is ready. I need to re-check my thinking
and test it somehow...
- remove kthreadd_task initialization from rest_init()
- change kthreadd() to initialize kthreadd_task = current
- change the main loop in kthreadd() to take kthread_create_lock
before the first schedule() (just shift schedule() down)
This way, if kthreadd_task needs the wakeup, kthread_create()
must see kthreadd_task != NULL after unlock(kthread_create_lock).
If kthread_create() sees kthreadd_task == NULL we can just sleep
on create.done, kthreadd() must notice the new request before
it calls schedule().
Note that with this change it is possible to use kthread_create()
at any time, but the caller will sleep until rest_init() creates
kthreadd.
Oleg.
init/main.c | 5 +----
kernel/kthread.c | 30 ++++++++++++++++++------------
2 files changed, 19 insertions(+), 16 deletions(-)
--- a/init/main.c
+++ b/init/main.c
@@ -449,12 +449,9 @@ static void __init setup_command_line(ch
static noinline void __init_refok rest_init(void)
__releases(kernel_lock)
{
- int pid;
-
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
- pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
- kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
+ kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
unlock_kernel();
/*
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -128,8 +128,14 @@ struct task_struct *kthread_create(int (
spin_lock(&kthread_create_lock);
list_add_tail(&create.list, &kthread_create_list);
spin_unlock(&kthread_create_lock);
-
- wake_up_process(kthreadd_task);
+ /*
+ * If kthreadd was not created yet, kthreadd() must see the result
+ * of list_add_tail() later, it takes kthread_create_lock before the
+ * first schedule(). If kthreadd() locked kthread_create_lock at
+ * least once, we must see kthreadd_task != NULL.
+ */
+ if (likely(kthreadd_task))
+ wake_up_process(kthreadd_task);
wait_for_completion(&create.done);
if (!IS_ERR(create.result)) {
@@ -216,23 +222,18 @@ EXPORT_SYMBOL(kthread_stop);
int kthreadd(void *unused)
{
- struct task_struct *tsk = current;
+ kthreadd_task = current;
/* Setup a clean context for our children to inherit. */
- set_task_comm(tsk, "kthreadd");
- ignore_signals(tsk);
- set_user_nice(tsk, KTHREAD_NICE_LEVEL);
- set_cpus_allowed_ptr(tsk, cpu_all_mask);
+ set_task_comm(kthreadd_task, "kthreadd");
+ ignore_signals(kthreadd_task);
+ set_user_nice(kthreadd_task, KTHREAD_NICE_LEVEL);
+ set_cpus_allowed_ptr(kthreadd_task, cpu_all_mask);
set_mems_allowed(node_possible_map);
current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
- if (list_empty(&kthread_create_list))
- schedule();
- __set_current_state(TASK_RUNNING);
-
spin_lock(&kthread_create_lock);
while (!list_empty(&kthread_create_list)) {
struct kthread_create_info *create;
@@ -247,6 +248,11 @@ int kthreadd(void *unused)
spin_lock(&kthread_create_lock);
}
spin_unlock(&kthread_create_lock);
+
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (list_empty(&kthread_create_list))
+ schedule();
+ __set_current_state(TASK_RUNNING);
}
return 0;
--
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