linux-kernel - Re: [PATCH] swiotlb: Fix unexpected swiotlb_alloc

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Date:   Tue, 10 Apr 2018 19:07:46 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Christian König <christian.koenig@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] swiotlb: Fix unexpected swiotlb_alloc_coherent()   failures

On Tue, 10 Apr 2018 19:06:15 +0200,
Christoph Hellwig wrote:
> 
> 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?

That I have no idea, sorry.  I just figured out the regression just
from the dmesg output of 4.16 kernel in bugzilla reports.
Could you take a look at the bugzilla reports there?


thanks,

Takashi

> > 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@...r.kernel.org> # v4.16+
> > Signed-off-by: Takashi Iwai <tiwai@...e.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---
>