linux-kernel - Re: [PATCH v3 1/3] memory: tegra: Add devm_tegra_get_memory

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Message-ID: <257958e0-8359-4296-9653-ba821b39d813@gmail.com>
Date:   Wed, 30 Sep 2020 18:22:37 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Nicolin Chen <nicoleotsuka@...il.com>, thierry.reding@...il.com,
        joro@...tes.org, vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] memory: tegra: Add
 devm_tegra_get_memory_controller()

30.09.2020 17:45, Krzysztof Kozlowski пишет:
> On Wed, 30 Sep 2020 at 16:41, Dmitry Osipenko <digetx@...il.com> wrote:
>>
>> ...
>>> +struct tegra_mc *devm_tegra_get_memory_controller(struct device *dev)
>>> +{
>>> +     struct platform_device *pdev;
>>> +     struct device_node *np;
>>> +     struct tegra_mc *mc;
>>> +     int err;
>>> +
>>> +     np = of_find_matching_node_and_match(NULL, tegra_mc_of_match, NULL);
>>> +     if (!np)
>>> +             return ERR_PTR(-ENOENT);
>>> +
>>> +     pdev = of_find_device_by_node(np);
>>> +     of_node_put(np);
>>> +     if (!pdev)
>>> +             return ERR_PTR(-ENODEV);
>>> +
>>> +     mc = platform_get_drvdata(pdev);
>>> +     if (!mc) {
>>> +             put_device(mc->dev);
>>
>> This should be put_device(&pdev->dev). Please always be careful while
>> copying someones else code :)
> 
> Good catch. I guess devm_add_action_or_reset() would also work... or
> running Smatch on new code. Smatch should point it out.

The devm_add_action_or_reset() shouldn't help much in this particular
case because it's too early for the devm_add_action here.

Having an explicit put_device() in all error code paths also helps with
improving readability of the code a tad, IMO.

Smatch indeed should catch this bug, but Smatch usually isn't a part of
the developers workflow. More often Smatch is a part of maintainers
workflow, hence such problems usually are getting caught before patches
are applied.