linux-kernel - Re: [PATCH 2/2] dmatest: check for dma mapping error

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Message-Id: <20121214003328.46cba41c.akpm@linux-foundation.org>
Date:	Fri, 14 Dec 2012 00:33:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vinod Koul <vinod.koul@...el.com>
Subject: Re: [PATCH 2/2] dmatest: check for dma mapping error

On Fri, 14 Dec 2012 09:06:03 +0200 Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Fri, Dec 14, 2012 at 1:34 AM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > On Mon, 10 Dec 2012 13:37:44 +0200
> > Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> >
> >> We get a warning if CONFIG_DMA_API_DEBUG=y
> >>
> >> [   28.150631] WARNING: at lib/dma-debug.c:933 check_unmap+0x5d6/0x6ac()
> >> [   28.157058] dw_dmac dw_dmac.0: DMA-API: device driver failed to check map error[device address=0x0000000035698305] [size=14365 bytes] [mapped as single]
> 
> >> --- a/drivers/dma/dmatest.c
> >> +++ b/drivers/dma/dmatest.c
> >> @@ -378,15 +378,35 @@ static int dmatest_func(void *data)
> >>
> >>                       dma_srcs[i] = dma_map_single(dev->dev, buf, len,
> >>                                                    DMA_TO_DEVICE);
> >> +                     ret = dma_mapping_error(dev->dev, dma_srcs[i]);
> >> +                     if (ret) {
> >> +                             unmap_src(dev->dev, dma_srcs, len, i);
> >> +                             pr_warn("%s: #%u: mapping error %d with "
> >> +                                     "src_off=0x%x len=0x%x\n",
> >> +                                     thread_name, total_tests - 1, ret,
> >> +                                     src_off, len);
> >> +                             failed_tests++;
> >> +                             continue;
> >> +                     }
> >
> > The changelog and the code don't match.  Which one is out of date?
> 
> I'm afraid I didn't get what is wrong.
> 

The above code will not emit the string "dw_dmac dw_dmac.0: DMA-API:
device driver failed to check map error[device
address=0x0000000035698305] [size=14365 bytes] [mapped as single]".

Oh I see what you did.  That string is emitted by the kernel at
present, and the patch prevents this.  And it also emits a new warning
if the mapping attempt failed, and that new warning wasn't described.

I updated the changelog:


: The kernel emits a warning if CONFIG_DMA_API_DEBUG=y:
: 
: [   28.150631] WARNING: at lib/dma-debug.c:933 check_unmap+0x5d6/0x6ac()
: [   28.157058] dw_dmac dw_dmac.0: DMA-API: device driver failed to check map error[device address=0x0000000035698305] [size=14365 bytes] [mapped as single]
: 
: Fix this by adding the required checking of the dma_map_single() return
: value.

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