linux-kernel - Re: [PATCH 27/31] usb/gadget/snps_udc_core: Move timer initialization earlier

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Message-ID: <xa1ttw0jwkpn.fsf@mina86.com>
Date:   Sun, 03 Sep 2017 23:12:04 +0200
From:   Michal Nazarewicz <mina86@...a86.com>
To:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>, Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Raviteja Garimella <raviteja.garimella@...adcom.com>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 27/31] usb/gadget/snps_udc_core: Move timer initialization earlier

On Thu, Aug 31 2017, Kees Cook wrote:
> With timer initialization made earlier at the start, there is no reason
> to make del_timer_sync() calls conditionally, there by removing the
> assignments and tests of the .data field.
>
> Cc: Felipe Balbi <balbi@...nel.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Raviteja Garimella <raviteja.garimella@...adcom.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: "Gustavo A. R. Silva" <garsilva@...eddedor.com>
> Cc: linux-usb@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/usb/gadget/udc/snps_udc_core.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/snps_udc_core.c b/drivers/usb/gadget/udc/snps_udc_core.c
> index 5460e5ba1c3c..1607e901e16b 100644
> --- a/drivers/usb/gadget/udc/snps_udc_core.c
> +++ b/drivers/usb/gadget/udc/snps_udc_core.c
> @@ -3067,14 +3067,12 @@ void udc_remove(struct udc *dev)
>  	stop_timer++;
>  	if (timer_pending(&udc_timer))
>  		wait_for_completion(&on_exit);
> -	if (udc_timer.data)
> -		del_timer_sync(&udc_timer);
> +	del_timer_sync(&udc_timer);
>  	/* remove pollstall timer */
>  	stop_pollstall_timer++;
>  	if (timer_pending(&udc_pollstall_timer))
>  		wait_for_completion(&on_pollstall_exit);
> -	if (udc_pollstall_timer.data)
> -		del_timer_sync(&udc_pollstall_timer);
> +	del_timer_sync(&udc_pollstall_timer);
>  	udc = NULL;
>  }
>  EXPORT_SYMBOL_GPL(udc_remove);
> @@ -3164,9 +3162,9 @@ int udc_probe(struct udc *dev)
>  	u32		reg;
>  	int		retval;
>  
> -	/* mark timer as not initialized */
> -	udc_timer.data = 0;
> -	udc_pollstall_timer.data = 0;
> +	/* timer init */
> +	setup_timer(&udc_timer, udc_timer_function, 0);
> +	setup_timer(&udc_pollstall_timer, udc_pollstall_timer_function, 0);
>  
>  	/* device struct setup */
>  	dev->gadget.ops = &udc_ops;
> @@ -3206,10 +3204,6 @@ int udc_probe(struct udc *dev)
>  	if (retval)
>  		goto finished;
>  
> -	/* timer init */
> -	setup_timer(&udc_timer, udc_timer_function, 1);
> -	setup_timer(&udc_pollstall_timer, udc_pollstall_timer_function, 1);
> -
>  	/* set SD */
>  	reg = readl(&dev->regs->ctl);
>  	reg |= AMD_BIT(UDC_DEVCTL_SD);


Stupid question, is the check in udc_remove even necessary?

udc_probe is called from udc_plat_probe:

	if (udc_probe(udc)) {
		ret = -ENODEV;
		goto exit_dma;
	}

If the call fails, udc_plat_probe cleans up after itself and noticeably
*does not* call udc_remove.  As far as I understand, if probe callback
fails, remove callback is *not* called.  Meanwhile, udc_remove is called
from the remove callback which is udc_plat_remove.  So, udc_remove can
be called only if udc_probe succeeds.

It seems to me that a better patch is:

--- a/drivers/usb/gadget/udc/snps_udc_core.c
+++ b/drivers/usb/gadget/udc/snps_udc_core.c
@@ -3067,14 +3067,12 @@ void udc_remove(struct udc *dev)
 	stop_timer++;
 	if (timer_pending(&udc_timer))
 		wait_for_completion(&on_exit);
-	if (udc_timer.data)
-		del_timer_sync(&udc_timer);
+	del_timer_sync(&udc_timer);
 	/* remove pollstall timer */
 	stop_pollstall_timer++;
 	if (timer_pending(&udc_pollstall_timer))
 		wait_for_completion(&on_pollstall_exit);
-	if (udc_pollstall_timer.data)
-		del_timer_sync(&udc_pollstall_timer);
+	del_timer_sync(&udc_pollstall_timer);
 	udc = NULL;
 }
 EXPORT_SYMBOL_GPL(udc_remove);
@@ -3164,9 +3162,9 @@ int udc_probe(struct udc *dev)
 	u32		reg;
 	int		retval;
 
-	/* mark timer as not initialized */
-	udc_timer.data = 0;
-	udc_pollstall_timer.data = 0;
-
 	/* device struct setup */
 	dev->gadget.ops = &udc_ops;

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»