linux-kernel - Re: [PATCH] usb: gadget: mass_storage: Make use of the helper macro kthread

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Date:   Thu, 21 Oct 2021 11:13:27 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Cai Huoqing <caihuoqing@...du.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: mass_storage: Make use of the helper macro
 kthread_run()

On Thu, Oct 21, 2021 at 04:43:58PM +0800, Cai Huoqing wrote:
> Repalce kthread_create/wake_up_process() with kthread_run()
> to simplify the code.
> 
> Signed-off-by: Cai Huoqing <caihuoqing@...du.com>
> ---
>  drivers/usb/gadget/function/f_mass_storage.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
> index 3cabf7692ee1..1e3cab5d635c 100644
> --- a/drivers/usb/gadget/function/f_mass_storage.c
> +++ b/drivers/usb/gadget/function/f_mass_storage.c
> @@ -2962,7 +2962,7 @@ static int fsg_bind(struct usb_configuration *c, struct usb_function *f)
>  	if (!common->thread_task) {
>  		common->state = FSG_STATE_NORMAL;
>  		common->thread_task =
> -			kthread_create(fsg_main_thread, common, "file-storage");
> +			kthread_run(fsg_main_thread, common, "file-storage");
>  		if (IS_ERR(common->thread_task)) {
>  			ret = PTR_ERR(common->thread_task);
>  			common->thread_task = NULL;
> @@ -2971,7 +2971,6 @@ static int fsg_bind(struct usb_configuration *c, struct usb_function *f)
>  		}
>  		DBG(common, "I/O thread pid: %d\n",
>  		    task_pid_nr(common->thread_task));
> -		wake_up_process(common->thread_task);
>  	}

We better not apply this patch for the same reason as the other one: 
It's probably not a good idea for the fsg_main_thread task to start 
running before common->thread_task has been assigned.

Alan Stern