Re: [PATCH] swiotlb: Fix unexpected swiotlb_alloc_coherent() failures

[Christoph Hellwig <hch@lst.de>]

On Tue, Apr 10, 2018 at 07:05:13PM +0200, Takashi Iwai wrote:
> The code refactoring by commit 0176adb00406 ("swiotlb: refactor
> coherent buffer allocation") made swiotlb_alloc_buffer() almost always
> failing due to a thinko: namely, the function evaluates the
> dma_coherent_ok() call incorrectly and dealing as if it's invalid.
> This ends up with weird errors like iwlwifi probe failure or amdgpu
> screen flickering.
> 
> This patch corrects the logic error.

This looks ok, although even hitting this code is a bad sign.  Do you
know why the previous dma_direct_alloc didn't succeed?

> 
> Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088658
> Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088902
> Fixes: 0176adb00406 ("swiotlb: refactor coherent buffer allocation")
> Cc: <stable@vger.kernel.org> # v4.16+
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
>  lib/swiotlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 47aeb04c1997..de7cc540450f 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -719,7 +719,7 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  		goto out_warn;
>  
>  	*dma_handle = __phys_to_dma(dev, phys_addr);
> -	if (dma_coherent_ok(dev, *dma_handle, size))
> +	if (!dma_coherent_ok(dev, *dma_handle, size))
>  		goto out_unmap;
>  
>  	memset(phys_to_virt(phys_addr), 0, size);
> -- 
> 2.16.3
---end quoted text---