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SubjectRe: [rfcomm_run] WARNING: CPU: 1 PID: 79 at kernel/sched/core.c:7156 __might_sleep()
On 10/03, Oleg Nesterov wrote:
>
> OK, this is fixable. rfcomm_run() can do
>
> add_wait_queue(&rfcomm_wq, &wait);
> while (!kthread_should_stop()) {
> rfcomm_process_sessions();
>
> set_kthread_wants_signal(true);
> wait_woken(TASK_INTERRUPTIBLE);
> set_kthread_wants_signal(false);
> }
> remove_wait_queue(&rfcomm_wq, &wait);

And in this case set_kthread_wants_signal(true) needs to avoid the races
with kthread_stop() too. See the hopefully complete patch at the end.

However,

> Or. perhaps we can change wait_woken
>
> - set_current_state(mode);
> + if (mode)
> + set_current_state(mode);
>
>
> then rfcomm_run() can do
>
> for (;;) {
> rfcomm_process_sessions();
>
> set_current_state(TASK_INTERRUPTIBLE);
> if (kthread_should_stop())
> break;
> wait_woken(0);
> }
>
> Or perhaps we can split wait_woken() into 2 helpers,
>
> static inline long wait_woken(wq, mode, timeout)
> {
> set_current_state(mode);
> schedule_woken(wq, timeout); // does the rest
> }
>
> to avoid "mode == 0" hack; rfcomm_run() should use schedule_woken().

probably this makes more sense in this particular case...

Oleg.
---

--- x/kernel/kthread.c
+++ x/kernel/kthread.c
@@ -48,6 +48,7 @@ struct kthread {

enum KTHREAD_BITS {
KTHREAD_IS_PER_CPU = 0,
+ KTHREAD_WANTS_SIGNAL,
KTHREAD_SHOULD_STOP,
KTHREAD_SHOULD_PARK,
KTHREAD_IS_PARKED,
@@ -442,6 +443,45 @@ int kthread_park(struct task_struct *k)
return ret;
}

+void set_kthread_wants_signal(bool on)
+{
+ struct kthread *kthread = to_kthread(current);
+ unsigned long flags;
+
+ spin_lock_irqsave(&current->sighand->siglock, flags);
+ if (on) {
+ set_bit(KTHREAD_WANTS_SIGNAL, &kthread->flags);
+ smp_mb__after_atomic();
+ if (kthread_should_stop())
+ set_thread_flag(TIF_SIGPENDING);
+ } else {
+ clear_bit(KTHREAD_WANTS_SIGNAL, &kthread->flags);
+ recalc_sigpending();
+ }
+ spin_unlock_irqrestore(&current->sighand->siglock, flags);
+}
+
+static void kthread_kill(struct task_struct *k, struct kthread *kthread)
+{
+ smp_mb__before_atomic();
+ if (test_bit(KTHREAD_WANTS_SIGNAL, &kthread->flags)) {
+ unsigned long flags;
+ bool kill = true;
+
+ if (lock_task_sighand(k, &flags)) {
+ kill = test_bit(KTHREAD_WANTS_SIGNAL, &kthread->flags);
+ if (kill)
+ signal_wake_up(k, 0);
+ unlock_task_sighand(k, &flags);
+ }
+
+ if (kill)
+ return;
+ }
+
+ wake_up_process(k);
+}
+
/**
* kthread_stop - stop a thread created by kthread_create().
* @k: thread created by kthread_create().
@@ -469,7 +509,7 @@ int kthread_stop(struct task_struct *k)
if (kthread) {
set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
__kthread_unpark(k, kthread);
- wake_up_process(k);
+ kthread_kill(k, kthread);
wait_for_completion(&kthread->exited);
}
ret = k->exit_code;


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