linux-kernel - Re: [PATCH 15/15] dma-mapping: bypass indirect calls for dma-direct

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Message-ID: <20181220164418.GA18777@ulmo>
Date:   Thu, 20 Dec 2018 17:44:18 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Keith Busch <keith.busch@...el.com>,
        Jonathan Derrick <jonathan.derrick@...el.com>,
        linux-pci@...r.kernel.org, linux-ia64@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/15] dma-mapping: bypass indirect calls for dma-direct

On Fri, Dec 07, 2018 at 11:07:20AM -0800, Christoph Hellwig wrote:
[...]
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 0b18cfbdde95..fc84c81029d9 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
[...]
> @@ -397,9 +404,9 @@ int dma_supported(struct device *dev, u64 mask)
>  {
>  	const struct dma_map_ops *ops = get_dma_ops(dev);
>  
> -	if (!ops)
> -		return 0;
> -	if (!ops->dma_supported)
> +	if (dma_is_direct(ops))
> +		return dma_direct_supported(dev, mask);
> +	if (ops->dma_supported)
>  		return 1;
>  	return ops->dma_supported(dev, mask);
>  }

Hi Christoph,

This hunk causes a crash on boot for me. It looks like a ! got lost in
the rework here. The following patch fixes the crash for me and restores
the logic of the op->dma_supported check.

Feel free to squash this patch into the above if you prefer that.

Thierry

--- >8 ---
From c502b29ab01fa857e81c78cd574d4d22d7d20e09 Mon Sep 17 00:00:00 2001
From: Thierry Reding <treding@...dia.com>
Date: Thu, 20 Dec 2018 17:35:47 +0100
Subject: [PATCH] dma-mapping: Fix inverted logic in dma_supported()

The cleanup in commit 356da6d0cde3 ("dma-mapping: bypass indirect calls
for dma-direct") accidentally inverted the logic in the check for the
presence of a ->dma_supported() callback. Switch this back to the way it
was to prevent a crash on boot.

Fixes: 356da6d0cde3 ("dma-mapping: bypass indirect calls for dma-direct")
Signed-off-by: Thierry Reding <treding@...dia.com>
---
 kernel/dma/mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index fc84c81029d9..d7c34d2d1ba5 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -406,7 +406,7 @@ int dma_supported(struct device *dev, u64 mask)
 
 	if (dma_is_direct(ops))
 		return dma_direct_supported(dev, mask);
-	if (ops->dma_supported)
+	if (!ops->dma_supported)
 		return 1;
 	return ops->dma_supported(dev, mask);
 }
-- 
2.19.1

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