linux-kernel - Re: [PATCH] USB: gadget: udc: s3c2410_udc: Remove pointless NULL check in s3c2410_udc

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Date:   Thu, 23 Apr 2020 11:10:25 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH] USB: gadget: udc: s3c2410_udc: Remove pointless NULL
 check in s3c2410_udc_nuke

On Thu, Apr 23, 2020 at 9:30 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang warns:
>
> drivers/usb/gadget/udc/s3c2410_udc.c:255:11: warning: comparison of
> address of 'ep->queue' equal to a null pointer is always false
> [-Wtautological-pointer-compare]
>         if (&ep->queue == NULL)
>              ~~~~^~~~~    ~~~~
> 1 warning generated.
>
> It is not wrong, queue is not a pointer so if ep is not NULL, the
> address of queue cannot be NULL. No other driver does a check like this
> and this check has been around since the driver was first introduced,
> presumably with no issues so it does not seem like this check should be
> something else. Just remove it.
>
> Commit afe956c577b2d ("kbuild: Enable -Wtautological-compare") exposed
> this but it is not the root cause of the warning.
>
> Fixes: 3fc154b6b8134 ("USB Gadget driver for Samsung s3c2410 ARM SoC")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1004
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Thanks for the patch!  If anything, I'd be happy to see some more NULL
checks against `ep`, though the callers of s3c2410_udc_nuke() also
seem quite confident that the pointer is not NULL.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  drivers/usb/gadget/udc/s3c2410_udc.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/s3c2410_udc.c b/drivers/usb/gadget/udc/s3c2410_udc.c
> index 0507a2ca0f552..80002d97b59d8 100644
> --- a/drivers/usb/gadget/udc/s3c2410_udc.c
> +++ b/drivers/usb/gadget/udc/s3c2410_udc.c
> @@ -251,10 +251,6 @@ static void s3c2410_udc_done(struct s3c2410_ep *ep,
>  static void s3c2410_udc_nuke(struct s3c2410_udc *udc,
>                 struct s3c2410_ep *ep, int status)
>  {
> -       /* Sanity check */
> -       if (&ep->queue == NULL)
> -               return;
> -
>         while (!list_empty(&ep->queue)) {
>                 struct s3c2410_request *req;
>                 req = list_entry(ep->queue.next, struct s3c2410_request,
>
> base-commit: ae83d0b416db002fe95601e7f97f64b59514d936
> --
> 2.26.2
>
> --
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-- 
Thanks,
~Nick Desaulniers