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Subject: Re: [PATCH V4 2/2] scsi: ufshcd: Fix device links when BOOT WLUN
 fails to probe
From:   Adrian Hunter <adrian.hunter@intel.com>
To:     "Martin K . Petersen" <martin.petersen@oracle.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Saravana Kannan <saravanak@google.com>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        linux-scsi@vger.kernel.org, Avri Altman <avri.altman@wdc.com>,
        Bean Huo <huobean@gmail.com>, Can Guo <cang@codeaurora.org>,
        Asutosh Das <asutoshd@codeaurora.org>,
        Bart Van Assche <bvanassche@acm.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Rafael J . Wysocki" <rafael@kernel.org>
References: <20210716114408.17320-1-adrian.hunter@intel.com>
 <20210716114408.17320-3-adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Message-ID: <c78aac34-5c55-f6b6-3450-d5c3f09781fa@intel.com>
Date:   Wed, 4 Aug 2021 18:33:27 +0300
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Martin, perhaps you could consider picking up this patch if no one objects?


On 16/07/21 2:44 pm, Adrian Hunter wrote:
> Managed device links are deleted by device_del(). However it is possible to
> add a device link to a consumer before device_add(), and then discovering
> an error prevents the device from being used. In that case normally
> references to the device would be dropped and the device would be deleted.
> However the device link holds a reference to the device, so the device link
> and device remain indefinitely (unless the supplier is deleted).
> 
> For UFSHCD, 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.
> 
> Amend device link removal to accept removal of a link with an unregistered
> consumer device (suggested by Rafael), and fix UFSHCD by explicitly
> deleting the device link when SCSI destroys the SCSI device.
> 
> Fixes: b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>
> ---
>  drivers/base/core.c       |  2 ++
>  drivers/scsi/ufs/ufshcd.c | 23 +++++++++++++++++++++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 2de8f7d8cf54..983e895d4ced 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -887,6 +887,8 @@ 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->kref);
>  	else
>  		WARN(1, "Unable to drop a managed device link reference\n");
>  }
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 708b3b62fc4d..9864a8ee0263 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -5020,15 +5020,34 @@ static int ufshcd_slave_configure(struct scsi_device *sdev)
>  static void ufshcd_slave_destroy(struct scsi_device *sdev)
>  {
>  	struct ufs_hba *hba;
> +	unsigned long flags;
>  
>  	hba = shost_priv(sdev->host);
>  	/* Drop the reference as it won't be needed anymore */
>  	if (ufshcd_scsi_to_upiu_lun(sdev->lun) == UFS_UPIU_UFS_DEVICE_WLUN) {
> -		unsigned long flags;
> -
>  		spin_lock_irqsave(hba->host->host_lock, flags);
>  		hba->sdev_ufs_device = NULL;
>  		spin_unlock_irqrestore(hba->host->host_lock, flags);
> +	} else if (hba->sdev_ufs_device) {
> +		struct device *supplier = NULL;
> +
> +		/* Ensure UFS Device WLUN exists and does not disappear */
> +		spin_lock_irqsave(hba->host->host_lock, flags);
> +		if (hba->sdev_ufs_device) {
> +			supplier = &hba->sdev_ufs_device->sdev_gendev;
> +			get_device(supplier);
> +		}
> +		spin_unlock_irqrestore(hba->host->host_lock, flags);
> +
> +		if (supplier) {
> +			/*
> +			 * 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_link_remove(&sdev->sdev_gendev, supplier);
> +			put_device(supplier);
> +		}
>  	}
>  }
>  
>