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

Hans de Goede
2021-06-10T09:49:09Z

Hi,

On 6/10/21 11:43 AM, 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().

As mentioned in the commit message, in input_unregister_device
is not necessary for input-devices created with
devm_input_allocate_device():

"According to the input documentation the input device allocated by
devm_input_allocate_device() does not need to be explicitly unregistered."

I have verified that the documentation is correct here, so there is
no need to keep the input_unregister_device() as it was never necessary
to have that there.

Regards,

Hans

>
>> -
>> - return 0;
>> -}
>> -
>> static struct platform_driver max77693_muic_driver = {
>> .driver = {
>> .name = DEV_NAME,
>> },
>> .probe = max77693_muic_probe,
>> - .remove = max77693_muic_remove,
>> };
>>
>> module_platform_driver(max77693_muic_driver);
>>
>