linux-kernel - Re: [PATCH] usb: storage: Replace mdelay with msleep in init

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Message-ID: <Pine.LNX.4.44L0.1804101014460.3142-100000@iolanthe.rowland.org>
Date:   Tue, 10 Apr 2018 10:15:06 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
cc:     gregkh@...uxfoundation.org, <linux-usb@...r.kernel.org>,
        <usb-storage@...ts.one-eyed-alien.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: storage: Replace mdelay with msleep in init_freecom

On Tue, 10 Apr 2018, Jia-Ju Bai wrote:

> init_freecom() is never called in atomic context.
> 
> init_freecom() is set as ".initFunction" through UNUSUAL_DEV().
> And ->initFunction() is only called by usb_stor_acquire_resources(), 
> which is only called by usb_stor_probe2().
> usb_stor_probe2() is called by *_probe() functions (like alauda_probe()) 
> for each USB driver.
> *_probe() functions are set ".probe" in struct usb_driver.
> These functions are not called in atomic context.
> 
> Despite never getting called from atomic context, init_freecom()
> calls mdelay() to busily wait.
> This is not necessary and can be replaced with msleep() to
> avoid busy waiting.
> 
> This is found by a static analysis tool named DCNS written by myself.
> And I also manually check it.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>

Acked-by: Alan Stern <stern@...land.harvard.edu>


> ---
>  drivers/usb/storage/freecom.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/storage/freecom.c b/drivers/usb/storage/freecom.c
> index c0a5d95..c7f886d 100644
> --- a/drivers/usb/storage/freecom.c
> +++ b/drivers/usb/storage/freecom.c
> @@ -477,7 +477,7 @@ static int init_freecom(struct us_data *us)
>  	usb_stor_dbg(us, "result from activate reset is %d\n", result);
>  
>  	/* wait 250ms */
> -	mdelay(250);
> +	msleep(250);
>  
>  	/* clear reset */
>  	result = usb_stor_control_msg(us, us->send_ctrl_pipe,
> @@ -485,7 +485,7 @@ static int init_freecom(struct us_data *us)
>  	usb_stor_dbg(us, "result from clear reset is %d\n", result);
>  
>  	/* wait 3 seconds */
> -	mdelay(3 * 1000);
> +	msleep(3 * 1000);
>  
>  	return USB_STOR_TRANSPORT_GOOD;
>  }
>