linux-kernel - Re: [PATCH] vhost: use kthread

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Message-ID: <20150415115547-mutt-send-email-mst@redhat.com>
Date:	Wed, 15 Apr 2015 11:59:01 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Bandan Das <bsd@...hat.com>
Cc:	kvm@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost: use kthread_run macro

On Tue, Apr 14, 2015 at 05:32:34PM -0400, Bandan Das wrote:
> 
> Code Cleanup, kthread_run is a convenient wrapper
> around kthread_create() that even wakes up the process
> for us. Use it and remove no longer needed temp
> task_struct variable.
> 
> Signed-off-by: Bandan Das <bsd@...hat.com>
> ---
>  drivers/vhost/vhost.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 2ee2826..9ac66f7 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -366,7 +366,6 @@ EXPORT_SYMBOL_GPL(vhost_dev_has_owner);
>  /* Caller should have device mutex */
>  long vhost_dev_set_owner(struct vhost_dev *dev)
>  {
> -	struct task_struct *worker;
>  	int err;
>  
>  	/* Is there an owner already? */
> @@ -377,15 +376,12 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>  
>  	/* No owner, become one */
>  	dev->mm = get_task_mm(current);
> -	worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
> -	if (IS_ERR(worker)) {
> -		err = PTR_ERR(worker);
> +	dev->worker = kthread_run(vhost_worker, dev, "vhost-%d", current->pid);
> +	if (IS_ERR(dev->worker)) {
> +		err = PTR_ERR(dev->worker);
>  		goto err_worker;

If you do it like this, dev->worker is not initialized when thread
starts running.  As thread itself might queue entries using
vhost_work_queue, this seems wrong.

>  	}
>  
> -	dev->worker = worker;
> -	wake_up_process(worker);	/* avoid contributing to loadavg */
> -
>  	err = vhost_attach_cgroups(dev);
>  	if (err)
>  		goto err_cgroup;
> @@ -396,7 +392,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>  
>  	return 0;
>  err_cgroup:
> -	kthread_stop(worker);
> +	kthread_stop(dev->worker);
>  	dev->worker = NULL;
>  err_worker:
>  	if (dev->mm)
> -- 
> 2.1.0
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