Re: [PATCH] kthread: Unpark only parked kthreads (was Re: [syzbot] [wireguard?] WARNING in kthread_unpark (2))

[Hillf Danton]

On Wed, 11 Sep 2024 14:04:28 +0200 Frederic Weisbecker <frederic@xxxxxxxxxx>
> 
> Can you test the following?
> ---

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> From: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Date: Tue, 10 Sep 2024 22:10:19 +0200
> Subject: [PATCH] kthread: Unpark only parked kthreads
> 
> Calling into kthread unparking unconditionally is mostly harmless when
> the kthread is already unparked. The wake up is then simply ignored
> because the target is not in TASK_PARKED state.
> 
> However if the kthread is per CPU, the wake up is preceded by a call
> to kthread_bind() which expects the task to be inactive and in
> TASK_PARKED state, which obviously isn't the case if it is unparked.
> 
> As a result, calling kthread_stop() on an unparked per-cpu kthread
> triggers such a warning:
> 
> 	WARNING: CPU: 0 PID: 11 at kernel/kthread.c:525 __kthread_bind_mask kernel/kthread.c:525
> 	 <TASK>
> 	 kthread_stop+0x17a/0x630 kernel/kthread.c:707
> 	 destroy_workqueue+0x136/0xc40 kernel/workqueue.c:5810
> 	 wg_destruct+0x1e2/0x2e0 drivers/net/wireguard/device.c:257
> 	 netdev_run_todo+0xe1a/0x1000 net/core/dev.c:10693
> 	 default_device_exit_batch+0xa14/0xa90 net/core/dev.c:11769
> 	 ops_exit_list net/core/net_namespace.c:178 [inline]
> 	 cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:640
> 	 process_one_work kernel/workqueue.c:3231 [inline]
> 	 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
> 	 worker_thread+0x86d/0xd70 kernel/workqueue.c:3393
> 	 kthread+0x2f0/0x390 kernel/kthread.c:389
> 	 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> 	 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 	 </TASK>
> 
> Fix this with skipping unecessary unparking while stopping a kthread.
> 
> Reported-by: syzbot+943d34fa3cf2191e3068@xxxxxxxxxxxxxxxxxxxxxxxxx
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> ---
>  kernel/kthread.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index f7be976ff88a..5e2ba556aba8 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -623,6 +623,8 @@ void kthread_unpark(struct task_struct *k)
>  {
>  	struct kthread *kthread = to_kthread(k);
>  
> +	if (!test_bit(KTHREAD_SHOULD_PARK, &kthread->flags))
> +		return;
>  	/*
>  	 * Newly created kthread was parked when the CPU was offline.
>  	 * The binding was lost and we need to set it again.
> -- 
> 2.46.0


#syz test upstream master

--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -623,6 +623,8 @@ void kthread_unpark(struct task_struct *
 {
 	struct kthread *kthread = to_kthread(k);
 
+	if (!test_bit(KTHREAD_SHOULD_PARK, &kthread->flags))
+		return;
 	/*
 	 * Newly created kthread was parked when the CPU was offline.
 	 * The binding was lost and we need to set it again.
--