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

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Date:   Thu, 8 Jul 2021 17:17:13 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "open list:TARGET SUBSYSTEM" <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 <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 2/2] scsi: ufshcd: Fix device links when BOOT WLUN
 fails to probe

On 8/07/21 3:31 pm, Rafael J. Wysocki wrote:
> On Wed, Jul 7, 2021 at 7:49 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> 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.
> 
> Yes, this is allowed, but if you've added device links to a device
> object that is not going to be registered after all, you are
> responsible for doing the cleanup.
> 
> Why can't you call device_link_del() directly on those links?
> 
> Or device_link_remove() if you don't want to deal with link pointers?
> 

Those only work for DL_FLAG_STATELESS device links, but we use only
DL_FLAG_PM_RUNTIME | DL_FLAG_RPM_ACTIVE flags.