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 17:12:20 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 Thu, Jul 8, 2021 at 5:03 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Jul 8, 2021 at 4:17 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
> >
> > 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.
>
> So I'd probably modify device_link_remove() to check if the consumer
> device has been registered and run __device_link_del() directly
> instead of device_link_put_kref() if it hasn't.
>
> Or add an argument to it to force the removal.

Or even modify device_link_put_kref() like this:

 static void device_link_put_kref(struct device_link *link)
 {
          if (link->flags & DL_FLAG_STATELESS)
                  kref_put(&link->kref, __device_link_del);
+        else if (!device_is_registered(link->consumer))
+                __device_link_del(link);
          else
                 WARN(1, "Unable to drop a managed device link reference\n");
 }