linux-kernel - Re: [PATCH] drm: omapdrm: Do not use helper unininitialized in omap_fbdev

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Date:   Mon, 27 Feb 2023 10:01:50 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Nathan Chancellor <nathan@...nel.org>, tomba@...nel.org,
        airlied@...il.com, daniel@...ll.ch, javierm@...hat.com
Cc:     ndesaulniers@...gle.com, trix@...hat.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] drm: omapdrm: Do not use helper unininitialized in
 omap_fbdev_init()

Hi

Am 24.02.23 um 18:25 schrieb Nathan Chancellor:
> Clang warns (or errors with CONFIG_WERROR):
> 
>    ../drivers/gpu/drm/omapdrm/omap_fbdev.c:235:6: error: variable 'helper' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>            if (!fbdev)
>                ^~~~~~
>    ../drivers/gpu/drm/omapdrm/omap_fbdev.c:259:26: note: uninitialized use occurs here
>            drm_fb_helper_unprepare(helper);
>                                    ^~~~~~
>    ../drivers/gpu/drm/omapdrm/omap_fbdev.c:235:2: note: remove the 'if' if its condition is always false
>            if (!fbdev)
>            ^~~~~~~~~~~
>    ../drivers/gpu/drm/omapdrm/omap_fbdev.c:228:30: note: initialize the variable 'helper' to silence this warning
>            struct drm_fb_helper *helper;
>                                        ^
>                                         = NULL
>    1 error generated.
> 
> Return early, as there is nothing for the function to do if memory
> cannot be allocated. There is no point in adding another label to just
> emit the warning at the end of the function in this case, as memory
> allocation failures are already logged.
> 
> Fixes: 3fb1f62f80a1 ("drm/fb-helper: Remove drm_fb_helper_unprepare() from drm_fb_helper_fini()")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1809
> Link: https://lore.kernel.org/oe-kbuild-all/202302250058.fYTe9aTP-lkp@intel.com/
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

> ---
> This is currently showing in mainline so I believe this should go to
> drm-misc-next-fixes.

This tree is only active from -rc6 to sometime during the merge window. 
I'll add your patch to drm-misc-fixes ASAP.

Best regards
Thomas

> ---
>   drivers/gpu/drm/omapdrm/omap_fbdev.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
> index 84429728347f..a6c8542087ec 100644
> --- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
> +++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
> @@ -233,7 +233,7 @@ void omap_fbdev_init(struct drm_device *dev)
>   
>   	fbdev = kzalloc(sizeof(*fbdev), GFP_KERNEL);
>   	if (!fbdev)
> -		goto fail;
> +		return;
>   
>   	INIT_WORK(&fbdev->work, pan_worker);
>   
> 
> ---
> base-commit: e034b8a18d4badceecb672c58b488bad1e901d95
> change-id: 20230224-omapdrm-wsometimes-uninitialized-0125f7692fbb
> 
> Best regards,

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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