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    SubjectRe: [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@kernel.org> wrote:
    >
    > On Thu, Jul 8, 2021 at 4:17 PM Adrian Hunter <adrian.hunter@intel.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@intel.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@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.
    > > >
    > > > 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");
    }

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