linux-kernel - Re: [PATCH 4.19 216/220] PM / devfreq: Fix static checker warning in try_then_request

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Date:   Thu, 28 Nov 2019 12:40:20 +0900
From:   Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 216/220] PM / devfreq: Fix static checker warning in
 try_then_request_governor

Hi,

On Fri, Nov 22, 2019 at 11:29:41AM +0100, Greg Kroah-Hartman wrote:
> From: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> 
> [ Upstream commit b53b0128052ffd687797d5f4deeb76327e7b5711 ]
> 
> The patch 23c7b54ca1cd: "PM / devfreq: Fix devfreq_add_device() when
> drivers are built as modules." leads to the following static checker
> warning:
> 
>     drivers/devfreq/devfreq.c:1043 governor_store()
>     warn: 'governor' can also be NULL
> 
> The reason is that the try_then_request_governor() function returns both
> error pointers and NULL. It should just return error pointers, so fix
> this by returning a ERR_PTR to the error intead of returning NULL.
> 
> Fixes: 23c7b54ca1cd ("PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
> Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

The following commits are provided for this fix:

commit 7544fd7f384591038646d3cd9efb311ab4509e24
Author: Ezequiel Garcia <ezequiel@...labora.com>
Date:   Fri Jun 21 18:39:49 2019 -0300

    PM / devfreq: Fix kernel oops on governor module load

    A bit unexpectedly (but still documented), request_module may
    return a positive value, in case of a modprobe error.
    This is currently causing issues in the devfreq framework.

    When a request_module exits with a positive value, we currently
    return that via ERR_PTR. However, because the value is positive,
    it's not a ERR_VALUE proper, and is therefore treated as a
    valid struct devfreq_governor pointer, leading to a kernel oops.

    Fix this by returning -EINVAL if request_module returns a positive
    value.

    Fixes: b53b0128052ff ("PM / devfreq: Fix static checker warning in try_then_request_governor")
    Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
    Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
    Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>

Please apply.

Best regards,
  Nobuhiro