linux-kernel - Re: [PATCH] usb: typec: ucsi: acpi: Remove notifier before destroying handler

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Message-Id: <16c47819-dbcc-4a9d-9124-7d440cfbf1d6@app.fastmail.com>
Date:   Fri, 24 Mar 2023 08:50:19 -0400
From:   "Mark Pearson" <mpearson-lenovo@...ebb.ca>
To:     "Heikki Krogerus" <heikki.krogerus@...ux.intel.com>
Cc:     "Greg KH" <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: ucsi: acpi: Remove notifier before destroying handler

Hi Heikki,

On Thu, Mar 23, 2023, at 5:57 AM, Heikki Krogerus wrote:
> On Tue, Mar 21, 2023 at 03:01:36PM -0400, Mark Pearson wrote:
>> Was debugging another issue (since fixed) and noticed that the acpi
>> notify_handler should be removed before the ucsi object is destroyed.
>> 
>> This isn't fixing any issues that I'm aware of - but I assume could
>> potentially lead to a race condition if you were really unlucky?
>> 
>> Signed-off-by: Mark Pearson <mpearson-lenovo@...ebb.ca>
>> ---
>>  drivers/usb/typec/ucsi/ucsi_acpi.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/usb/typec/ucsi/ucsi_acpi.c b/drivers/usb/typec/ucsi/ucsi_acpi.c
>> index ce0c8ef80c04..be3bf4f996d3 100644
>> --- a/drivers/usb/typec/ucsi/ucsi_acpi.c
>> +++ b/drivers/usb/typec/ucsi/ucsi_acpi.c
>> @@ -176,12 +176,12 @@ static int ucsi_acpi_remove(struct platform_device *pdev)
>>  {
>>  	struct ucsi_acpi *ua = platform_get_drvdata(pdev);
>>  
>> -	ucsi_unregister(ua->ucsi);
>> -	ucsi_destroy(ua->ucsi);
>> -
>>  	acpi_remove_notify_handler(ACPI_HANDLE(&pdev->dev), ACPI_DEVICE_NOTIFY,
>>  				   ucsi_acpi_notify);
>>  
>> +	ucsi_unregister(ua->ucsi);
>> +	ucsi_destroy(ua->ucsi);
>> +
>>  	return 0;
>>  }
>
> Calling ucsi_desctroy() after removing the notifier makes sense to me,
> but do you also need to unregister the instance after that?
>
> You may still be in the middle of init or resume, so I think we need
> to accept notifications until we are sure those have finished, i.e.
> ucsi_unregister() has finished.
>

That makes sense - I hadn't considered that.
I'll post an updated patch with the acpi_remove_notify_handler between the two calls.

Thanks for the review
Mark