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SubjectRe: [PATCH] Intel: Skylake: Fix inconsistent IS_ERR and PTR_ERR
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On 2020-02-21 16:40, Pierre-Louis Bossart wrote:
> 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.

Please include all maintainers of given driver when submitting the
patch, thank you.

>> []
>>> 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.

Thanks for notifying, Pierre.

Although NAK is upheld here. Proposed change is likely to introduce
regression.

>
> 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.

As basically entire old Skylake code, so no surprises here : )
struct skl_clk_data::avail_clk_cnt field is initialized with 0 via
devm_kzalloc in skl_clk_dev_probe().

>
> 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?

Indeed, code looks wrong. Idk what are we even dropping in
unregister_src_clk() if register_skl_clk() fails and avail_clk_cnt gets
incremented anyway.

In general usage of while(ptr->counter--) (example of which is present
in unregister_src_clk()) is prone to errors. Decrementation happens
regardless of while's check outcome and caller may receive back handle
in invalid state.

Amadeo, your thoughts?

Czarek

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