linux-kernel - Re: [PATCH] ASoC: Intel: avoid Oops if DMA setup fails

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Message-ID: <20190429170219.GA89435@google.com>
Date:   Mon, 29 Apr 2019 11:02:19 -0600
From:   Ross Zwisler <zwisler@...gle.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Ross Zwisler <zwisler@...omium.org>, linux-kernel@...r.kernel.org,
        Jaroslav Kysela <perex@...ex.cz>,
        Jie Yang <yang.jie@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        alsa-devel@...a-project.org, stable@...r.kernel.org
Subject: Re: [PATCH] ASoC: Intel: avoid Oops if DMA setup fails

On Fri, Apr 26, 2019 at 04:03:47PM -0500, Pierre-Louis Bossart wrote:
> On 4/26/19 11:47 AM, Ross Zwisler wrote:
> > Currently in sst_dsp_new() if we get an error return from sst_dma_new()
> > we just print an error message and then still complete the function
> > successfully.  This means that we are trying to run without sst->dma
> > properly set up, which will result in NULL pointer dereference when
> > sst->dma is later used.  This was happening for me in
> > sst_dsp_dma_get_channel():
> > 
> >          struct sst_dma *dma = dsp->dma;
> > 	...
> >          dma->ch = dma_request_channel(mask, dma_chan_filter, dsp);
> > 
> > This resulted in:
> > 
> >     BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> >     IP: sst_dsp_dma_get_channel+0x4f/0x125 [snd_soc_sst_firmware]
> > 
> > Fix this by adding proper error handling for the case where we fail to
> > set up DMA.
> > 
> > Signed-off-by: Ross Zwisler <zwisler@...gle.com>
> > Cc: stable@...r.kernel.org
> > ---
> >   sound/soc/intel/common/sst-firmware.c | 6 +++++-
> >   1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/sound/soc/intel/common/sst-firmware.c b/sound/soc/intel/common/sst-firmware.c
> > index 1e067504b6043..9be3a793a55e3 100644
> > --- a/sound/soc/intel/common/sst-firmware.c
> > +++ b/sound/soc/intel/common/sst-firmware.c
> > @@ -1251,11 +1251,15 @@ struct sst_dsp *sst_dsp_new(struct device *dev,
> >   		goto irq_err;
> >   	err = sst_dma_new(sst);
> > -	if (err)
> > +	if (err)  {
> >   		dev_warn(dev, "sst_dma_new failed %d\n", err);
> > +		goto dma_err;
> > +	}
> 
> Thanks for the patch.
> The fix looks correct, but does it make sense to keep a dev_warn() here?
> Should it be changed to dev_err() instead since as you mentioned it's fatal
> to keep going.
> Also you may want to mention in the commit message that this should only
> impact Broadwell and maybe the legacy Baytrail driver. IIRC we don't use the
> DMAs in other cases.

Sure, I'll address both of these in a v2.  Thank you for the quick review.