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Subject: Re: [PATCH RFC 2/2] scsi: ufshcd: Fix device links when BOOT WLUN
 fails to probe
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Rafael J . Wysocki" <rafael@kernel.org>,
        Saravana Kannan <saravanak@google.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        linux-scsi@vger.kernel.org, Avri Altman <avri.altman@wdc.com>,
        Bean Huo <huobean@gmail.com>, Can Guo <cang@codeaurora.org>,
        Asutosh Das <asutoshd@codeaurora.org>,
        Bart Van Assche <bvanassche@acm.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210707172948.1025-1-adrian.hunter@intel.com>
 <20210707172948.1025-3-adrian.hunter@intel.com> <YOXm4FuL/CW4lYDZ@kroah.com>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
Message-ID: <66130101-b0c5-a9a3-318a-468c6f3b380f@intel.com>
Date:   Wed, 7 Jul 2021 20:49:58 +0300
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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@intel.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.