linux-kernel - Re: [PATCH 5.4 34/65] kthread: save thread function

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Date:   Tue, 7 Jul 2020 11:31:57 -0400
From:   "J. Bruce Fields" <bfields@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sasha Levin <sashal@...nel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 5.4 34/65] kthread: save thread function

NACK.--b.

On Tue, Jul 07, 2020 at 05:17:13PM +0200, Greg Kroah-Hartman wrote:
> From: J. Bruce Fields <bfields@...hat.com>
> 
> [ Upstream commit 52782c92ac85c4e393eb4a903a62e6c24afa633f ]
> 
> It's handy to keep the kthread_fn just as a unique cookie to identify
> classes of kthreads.  E.g. if you can verify that a given task is
> running your thread_fn, then you may know what sort of type kthread_data
> points to.
> 
> We'll use this in nfsd to pass some information into the vfs.  Note it
> will need kthread_data() exported too.
> 
> Original-patch-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: J. Bruce Fields <bfields@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  include/linux/kthread.h |  1 +
>  kernel/kthread.c        | 17 +++++++++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/include/linux/kthread.h b/include/linux/kthread.h
> index 0f9da966934e2..59bbc63ff8637 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -57,6 +57,7 @@ bool kthread_should_stop(void);
>  bool kthread_should_park(void);
>  bool __kthread_should_park(struct task_struct *k);
>  bool kthread_freezable_should_stop(bool *was_frozen);
> +void *kthread_func(struct task_struct *k);
>  void *kthread_data(struct task_struct *k);
>  void *kthread_probe_data(struct task_struct *k);
>  int kthread_park(struct task_struct *k);
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index b262f47046ca4..543dff6b576c7 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -46,6 +46,7 @@ struct kthread_create_info
>  struct kthread {
>  	unsigned long flags;
>  	unsigned int cpu;
> +	int (*threadfn)(void *);
>  	void *data;
>  	struct completion parked;
>  	struct completion exited;
> @@ -152,6 +153,20 @@ bool kthread_freezable_should_stop(bool *was_frozen)
>  }
>  EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
>  
> +/**
> + * kthread_func - return the function specified on kthread creation
> + * @task: kthread task in question
> + *
> + * Returns NULL if the task is not a kthread.
> + */
> +void *kthread_func(struct task_struct *task)
> +{
> +	if (task->flags & PF_KTHREAD)
> +		return to_kthread(task)->threadfn;
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(kthread_func);
> +
>  /**
>   * kthread_data - return data value specified on kthread creation
>   * @task: kthread task in question
> @@ -164,6 +179,7 @@ void *kthread_data(struct task_struct *task)
>  {
>  	return to_kthread(task)->data;
>  }
> +EXPORT_SYMBOL_GPL(kthread_data);
>  
>  /**
>   * kthread_probe_data - speculative version of kthread_data()
> @@ -237,6 +253,7 @@ static int kthread(void *_create)
>  		do_exit(-ENOMEM);
>  	}
>  
> +	self->threadfn = threadfn;
>  	self->data = data;
>  	init_completion(&self->exited);
>  	init_completion(&self->parked);
> -- 
> 2.25.1
> 
> 
>