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 14:31:13 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "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>,
        "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 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?