linux-kernel - Re: [PATCH RFC 2/2] scsi: ufshcd: Fix device links when BOOT WLUN fails to probe

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Date:   Wed, 7 Jul 2021 20:49:58 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        linux-scsi@...r.kernel.org, Avri Altman <avri.altman@....com>,
        Bean Huo <huobean@...il.com>, Can Guo <cang@...eaurora.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Bart Van Assche <bvanassche@....org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] scsi: ufshcd: Fix device links when BOOT WLUN
 fails to probe

On 7/07/21 8:39 pm, Greg Kroah-Hartman wrote:
> On Wed, Jul 07, 2021 at 08:29:48PM +0300, Adrian Hunter wrote:
>> If a LUN fails to probe (e.g. absent BOOT WLUN), the device will not have
>> been registered but can still have a device link holding a reference to the
>> device. The unwanted device link will prevent runtime suspend indefinitely,
>> and cause some warnings if the supplier is ever deleted (e.g. by unbinding
>> the UFS host controller). Fix by explicitly deleting the device link when
>> SCSI destroys the SCSI device.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index 708b3b62fc4d..483aa74fe2c8 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -5029,6 +5029,13 @@ static void ufshcd_slave_destroy(struct scsi_device *sdev)
>>  		spin_lock_irqsave(hba->host->host_lock, flags);
>>  		hba->sdev_ufs_device = NULL;
>>  		spin_unlock_irqrestore(hba->host->host_lock, flags);
>> +	} else {
>> +		/*
>> +		 * If a LUN fails to probe (e.g. absent BOOT WLUN), the device
>> +		 * will not have been registered but can still have a device
>> +		 * link holding a reference to the device.
>> +		 */
>> +		device_links_scrap(&sdev->sdev_gendev);
> 
> What created that link?  And why did it do that before probe happened
> successfully?

The same driver created the link.

The documentation seems to say it is allowed to, if it is the consumer.
>From Documentation/driver-api/device_link.rst

  Usage
  =====

  The earliest point in time when device links can be added is after
  :c:func:`device_add()` has been called for the supplier and
  :c:func:`device_initialize()` has been called for the consumer.