linux-kernel - Re: [PATCH] Intel: Skylake: Fix inconsistent IS_ERR and PTR

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Date:   Fri, 21 Feb 2020 09:40:13 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Joe Perches <joe@...ches.com>, Xu Wang <vulab@...as.ac.cn>,
        perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org
Cc:     linux-kernel@...r.kernel.org,
        "Rojewski, Cezary" <cezary.rojewski@...el.com>,
        "Slawinski, AmadeuszX" <amadeuszx.slawinski@...el.com>
Subject: Re: [PATCH] Intel: Skylake: Fix inconsistent IS_ERR and PTR_ERR



On 2/21/20 8:41 AM, Joe Perches wrote:
> On Fri, 2020-02-21 at 18:11 +0800, Xu Wang wrote:
>> PTR_ERR should access the value just tested by IS_ERR.
>> In skl_clk_dev_probe(),it is inconsistent.
> []
>> diff --git a/sound/soc/intel/skylake/skl-ssp-clk.c b/sound/soc/intel/skylake/skl-ssp-clk.c
> []
>> @@ -384,7 +384,7 @@ static int skl_clk_dev_probe(struct platform_device *pdev)
>>   				&clks[i], clk_pdata, i);
>>   
>>   		if (IS_ERR(data->clk[data->avail_clk_cnt])) {
>> -			ret = PTR_ERR(data->clk[data->avail_clk_cnt++]);
>> +			ret = PTR_ERR(data->clk[data->avail_clk_cnt]);
> 
> NAK.
> 
> This is not inconsistent and you are removing the ++
> which is a post increment.  Likely that is necessary.
> 
> You could write the access and the increment as two
> separate statements if it confuses you.

Well to be fair the code is far from clear.

the post-increment is likely needed because of the error handling in 
unregister_src_clk 1
		data->clk[data->avail_clk_cnt] = register_skl_clk(dev,
				&clks[i], clk_pdata, i);

		if (IS_ERR(data->clk[data->avail_clk_cnt])) {
			ret = PTR_ERR(data->clk[data->avail_clk_cnt++]);
			goto err_unreg_skl_clk;
		}
	}

	platform_set_drvdata(pdev, data);

	return 0;

err_unreg_skl_clk:
	unregister_src_clk(data);

static void unregister_src_clk(struct skl_clk_data *dclk)
{
	while (dclk->avail_clk_cnt--)
		clkdev_drop(dclk->clk[dclk->avail_clk_cnt]->lookup);
}

So the post-increment is cancelled in the while().

That said, the avail_clk_cnt field is never initialized or incremented 
in normal usages so the code looks quite suspicious indeed.

gitk tells me this patch is likely the culprit:

6ee927f2f01466 ('ASoC: Intel: Skylake: Fix NULL ptr dereference when 
unloading clk dev')

-		data->clk[i] = register_skl_clk(dev, &clks[i], clk_pdata, i);
-		if (IS_ERR(data->clk[i])) {
-			ret = PTR_ERR(data->clk[i]);
+		data->clk[data->avail_clk_cnt] = register_skl_clk(dev,
+				&clks[i], clk_pdata, i);
+
+		if (IS_ERR(data->clk[data->avail_clk_cnt])) {
+			ret = PTR_ERR(data->clk[data->avail_clk_cnt++]);
  			goto err_unreg_skl_clk;
  		}
-
-		data->avail_clk_cnt++;

That last removal is probably wrong. Cezary and Amadeusz, you may want 
to look at this?