Re: [PATCH RESEND v2 3/5] extcon: extcon-max77693.c: Fix potential work-queue cancellation race

From: Chanwoo Choi <cw00.choi@samsung.com>
To: matti.vaittinen@fi.rohmeurope.com
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	linux-kernel@vger.kernel.org,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>
Subject: Re: [PATCH RESEND v2 3/5] extcon: extcon-max77693.c: Fix potential work-queue cancellation race
Date: Fri, 11 Jun 2021 16:16:25 +0900	[thread overview]
Message-ID: <c2a97466-e341-de1d-3d44-60cafce9774f@samsung.com> (raw)
In-Reply-To: <5939eb35e75e9f1288042430c367650b2e8b2996.camel@fi.rohmeurope.com>

On 6/10/21 6:57 PM, Matti Vaittinen wrote:
> 
> On Thu, 2021-06-10 at 18:43 +0900, Chanwoo Choi wrote:
>> On 6/8/21 7:10 PM, Matti Vaittinen wrote:
>>> The extcon IRQ schedules a work item. IRQ is requested using devm
>>> while
>>> WQ is cancelld at remove(). This mixing of devm and manual
>>> unwinding has
>>> potential case where the WQ has been emptied (.remove() was ran)
>>> but
>>> devm unwinding of IRQ was not yet done. It may be possible the IRQ
>>> is
>>> triggered at this point scheduling new work item to the already
>>> flushed
>>> queue.
>>>
>>> According to the input documentation the input device allocated by
>>> devm_input_allocate_device() does not need to be explicitly
>>> unregistered.
>>> Use the new devm_work_autocancel() and remove the remove() to
>>> simplify the
>>> code.
>>>
>>> Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
>>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com
>>>>
>>> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
>>> ---
>>>
>>> Please note that the change is compile-tested only. All proper
>>> testing is
>>> highly appreciated.
>>> ---
>>>  drivers/extcon/extcon-max77693.c | 17 +++++------------
>>>  1 file changed, 5 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/extcon/extcon-max77693.c
>>> b/drivers/extcon/extcon-max77693.c
>>> index 92af97e00828..1f1d9ab0c5c7 100644
>>> --- a/drivers/extcon/extcon-max77693.c
>>> +++ b/drivers/extcon/extcon-max77693.c
>>> @@ -5,6 +5,7 @@
>>>  // Copyright (C) 2012 Samsung Electrnoics
>>>  // Chanwoo Choi <cw00.choi@samsung.com>
>>>  
>>> +#include <linux/devm-helpers.h>
>>>  #include <linux/kernel.h>
>>>  #include <linux/module.h>
>>>  #include <linux/i2c.h>
>>> @@ -1127,7 +1128,10 @@ static int max77693_muic_probe(struct
>>> platform_device *pdev)
>>>  	platform_set_drvdata(pdev, info);
>>>  	mutex_init(&info->mutex);
>>>  
>>> -	INIT_WORK(&info->irq_work, max77693_muic_irq_work);
>>> +	ret = devm_work_autocancel(&pdev->dev, &info->irq_work,
>>> +				   max77693_muic_irq_work);
>>> +	if (ret)
>>> +		return ret;
>>>  
>>>  	/* Support irq domain for MAX77693 MUIC device */
>>>  	for (i = 0; i < ARRAY_SIZE(muic_irqs); i++) {
>>> @@ -1254,22 +1258,11 @@ static int max77693_muic_probe(struct
>>> platform_device *pdev)
>>>  	return ret;
>>>  }
>>>  
>>> -static int max77693_muic_remove(struct platform_device *pdev)
>>> -{
>>> -	struct max77693_muic_info *info = platform_get_drvdata(pdev);
>>> -
>>> -	cancel_work_sync(&info->irq_work);
>>> -	input_unregister_device(info->dock);
>>
>> I think that you have to keep the input_unregister_device().
> 
> Are you sure? I can add back the remove() if required - but the
> kerneldoc for devm_input_allocate_device() seems to be suggesting that
> this would not be needed:
> 
>  * Managed input devices do not need to be explicitly unregistered or
>  * freed as it will be done automatically when owner device unbinds
> from
>  * its driver (or binding fails). Once managed input device is
> allocated,
>  * it is ready to be set up and registered in the same fashion as
> regular
>  * input device. There are no special devm_input_device_[un]register()
>  * variants, regular ones work with both managed and unmanaged devices,
>  * should you need them. In most cases however, managed input device
> need
>  * not be explicitly unregistered or freed.
> 
> https://protect2.fireeye.com/v1/url?k=ffe6f053-a07dc951-ffe77b1c-0cc47a312ab0-aa86636d08cba7ad&q=1&e=f8aab92a-f090-4b48-91f8-4dffa41042e9&u=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Fv5.13-rc5%2Fsource%2Fdrivers%2Finput%2Finput.c%23L1955
> 
> I am not going to argue with you though - I am not really familiar with
> the input subsystem. I'd appreciate if someone could shed some light on
> when the input_unregister_device() can be omitted? 

You're right. Thanks for pointing out.

Acked-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics