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

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Message-ID: <CAJZ5v0hXR+ZsjKP1BUrOEXDFfD3ha=w90bExrx5qhTrOG16Ksw@mail.gmail.com>
Date:   Thu, 8 Jul 2021 17:03:07 +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 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.