linux-kernel - Re: [PATCH v7 2/4] power: reset: add reboot mode driver

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Message-id: <57045F9D.1000502@samsung.com>
Date:	Wed, 06 Apr 2016 10:00:13 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Andy Yan <andy.yan@...k-chips.com>, robh+dt@...nel.org,
	sre@...nel.org, heiko@...ech.de, john.stultz@...aro.org,
	arnd@...db.de
Cc:	mark.rutland@....com, catalin.marinas@....com, will.deacon@....com,
	alexandre.belloni@...e-electrons.com, f.fainelli@...il.com,
	linux@....linux.org.uk, dbaryshkov@...il.com,
	linux-pm@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	wxt@...k-chips.com, devicetree@...r.kernel.org, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, lorenzo.pieralisi@....com,
	matthias.bgg@...il.com, linux-arm-kernel@...ts.infradead.org,
	moritz.fischer@...us.com, mbrugger@...e.com,
	linux-kernel@...r.kernel.org, galak@...eaurora.org, olof@...om.net,
	jun.nie@...aro.org, dwmw2@...radead.org
Subject: Re: [PATCH v7 2/4] power: reset: add reboot mode driver

On 06.04.2016 09:50, Andy Yan wrote:

(...)

>>> +            return -ENOMEM;
>>> +
>>> +        info->mode = kstrdup_const(prop->name + len, GFP_KERNEL);
>>> +        if (of_property_read_u32(np, prop->name, &info->magic)) {
>>> +            dev_err(dev, "reboot mode %s without magic number\n",
>>> +                info->mode);
>>> +            devm_kfree(dev, info);
>>> +            continue;
>>> +        }
>>> +        list_add_tail(&info->list, &reboot->head);
>>> +    }
>>> +    of_node_put(np);
>> If you of_node_put() here, there is no sense in getting it before. I
>> mentioned of_node_get() only because I am not sure about life-cycle of
>> nodes in case of DT overlays and you are storing the pointer to string
>> from DT.
>>
>> The doubts I have are concerning only the case of freeing nodes from
>> overlay.
>>
>> I don't know if of_node_get() is needed but of_node_get()+of_node_put()
>> seems useless.
> 
> 
>  I am also not sure about it. Maybe just drop of_node_get/put ?

OK, let's drop both get() and put().

(...)

>>> +
>>> +static const struct of_device_id syscon_reboot_mode_of_match[] = {
>>> +    { .compatible = "syscon-reboot-mode" },
>>> +    {}
>>> +};
>>> +
>>> +static struct platform_driver syscon_reboot_mode_driver = {
>>> +    .probe = syscon_reboot_mode_probe,
>> Cleanup needed. What will happen after device unbind? Memory will be
>> released (devm-*()) but reboot notifier won't thus leading to OOPS on
>> reboot.
> 
>     From the kernel_restart_prepare function, the reboot notifier will
> be called before device_shutdown. Is there any other case the device
> unbind before reboot notifier
> called?

This is a regular module platform driver so unbind can happen any time
initiated by user, either by unbind command or by module removal. User
can then re-bind device or not - probably does not matter. Anyway after
such first unbind, the restart will kaboom instead of do a restart.

Beside that, you always should clean up, regardless of restart or not.
If you do not want unbind (thus no need of cleanup) then forbid it by
making it a non-module with suppressed bind.

Best regards,
Krzysztof