linux-kernel - Re: [PATCH] work around warning in i915_gem_gtt

Open Source and information security mailing list archives

Message-ID: <20140728152448.GD4747@phenom.ffwll.local>
Date:	Mon, 28 Jul 2014 17:24:48 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Pavel Machek <pavel@....cz>
Cc:	daniel.vetter@...ll.ch, jani.nikula@...ux.intel.com,
	airlied@...ux.ie, intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] work around warning in i915_gem_gtt

On Mon, Jul 28, 2014 at 01:20:58PM +0200, Pavel Machek wrote:
> 
> Gcc warns that addr might be used uninitialized. It may not, but I see
> why gcc gets confused.
> 
> Additionally, hiding code with side-effects inside WARN_ON() argument
> seems uncool, so I moved it outside.
> 
> Signed-off-by: Pavel Machek <pavel@....cz>
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 8b3cde7..8fcc974 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -1448,7 +1448,7 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
>  		(gen6_gtt_pte_t __iomem *)dev_priv->gtt.gsm + first_entry;
>  	int i = 0;
>  	struct sg_page_iter sg_iter;
> -	dma_addr_t addr;
> +	dma_addr_t addr = 0;

I want to have a /* shuts up gcc */ for these kinds of things, where we
need to help out the compiler. Added and merged, thanks.
-Daniel

>  
>  	for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
>  		addr = sg_page_iter_dma_address(&sg_iter);
> @@ -1462,9 +1462,10 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
>  	 * of NUMA access patterns. Therefore, even with the way we assume
>  	 * hardware should work, we must keep this posting read for paranoia.
>  	 */
> -	if (i != 0)
> -		WARN_ON(readl(&gtt_entries[i-1]) !=
> -			vm->pte_encode(addr, level, true));
> +	if (i != 0) {
> +		unsigned long gtt = readl(&gtt_entries[i-1]);
> +		WARN_ON(gtt != vm->pte_encode(addr, level, true));
> +	}
>  
>  	/* This next bit makes the above posting read even more important. We
>  	 * want to flush the TLBs only after we're certain all the PTE updates
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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