Re: [PATCH v2 5/5] kthread: remove worker->task self assignment

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Removing the self-assignment `worker->task = current;` breaks out-of-tree (OOT) users of the old `kthread_run(kthread_worker_fn, ...)` API, causing them to permanently deadlock due to missed wakeups.
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commit 4e8323d40e4fe5053d4171cbca8193f9bd6080b8
Author: Bradley Morgan <brads@mainlining.org>

kthread: remove worker->task self assignment

All kthread worker users now create their workers with kthread_create_worker*(),
which sets worker->task before the worker starts. The self assignment in
kthread_worker_fn() is removed, leaving a warning check for out-of-tree users.

> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 63beb59b7a3d1..643407647e79d 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -987,12 +987,10 @@ int kthread_worker_fn(void *worker_ptr)
>  	struct kthread_worker *worker = worker_ptr;
>  	struct kthread_work *work;
>  
> -	/*
> -	 * FIXME: Update the check and remove the assignment when all kthread
> -	 * worker users are created using kthread_create_worker*() functions.
> +	/* All workers are created with worker->task set. If this fires,
> +	 * the caller is broken.
>  	 */
> -	WARN_ON(worker->task && worker->task != current);
> -	worker->task = current;
> +	WARN_ON(worker->task != current);

[Severity: Medium]
Does removing this assignment cause out-of-tree users of the old
kthread_run() API to hang permanently?

Because the self-assignment is removed, worker->task will remain NULL for any
callers still using the old API. When new work is inserted, the wakeup will be
silently skipped in kthread_insert_work():

kernel/kthread.c:kthread_insert_work() {
	...
	if (!worker->current_work && likely(worker->task))
		wake_up_process(worker->task);
	...
}

This means the warning intended as a sanity check turns into a silent, fatal
breakage where the worker hangs in TASK_INTERRUPTIBLE and queued work is never
processed.

>  
>  	if (worker->flags & KTW_FREEZABLE)
>  		set_freezable();

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1788513591.git.brads@mainlining.org?part=5