driver core: Add ability to delete device links of unregistered devices

PATCH Superseded Adrian Hunter 3 participants 7 messages Jul 9, 2021

Subsystems (2)

SCSI Driver core

lore

Share & tools

lore

Adrian Hunter

author

2021-07-09 06:43 UTC #0 lore raw

v2 cover driver core: Add ability to delete device links of unregistered devices

There is an issue with the SCSI UFS driver when the optional BOOT well-known LUN fails to probe, which is not a fatal error. The issue is that the device and its "managed" device link do not then get deleted. The device because the device link has a reference to it. The device link because it can only be deleted by device_del(), but device_add() was never called, so device_del() never will be either.

These V2 patches fix the issue by amending device link removal to accept removal of a link with an unregistered consumer device, as suggested by Rafael.

Changes in V2:

Take approach suggested by Rafael

Adrian Hunter (2):
driver core: Add ability to delete device links of unregistered devices
scsi: ufshcd: Fix device links when BOOT WLUN fails to probe

 drivers/base/core.c       | 11 ++++++++---
 drivers/scsi/ufs/ufshcd.c | 23 +++++++++++++++++++++--
 2 files changed, 29 insertions(+), 5 deletions(-)

Regards
Adrian

Adrian Hunter

author

2021-07-09 06:43 UTC #1 lore raw

PATCH v2 1/2 driver core: Add ability to delete device links of unregistered devices

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 discover 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.

Amend device link removal to accept removal of a link with an unregistered consumer device.

To make that work nicely, the devlink_remove_symlinks() function must be amended to cope with the absence of the consumer's sysfs presence, otherwise sysfs_remove_link() will generate a warning.

Fixes b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")

Signed-off-by Adrian Hunter <[email protected]>

---
 drivers/base/core.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

drivers/base/core.c +8 -3

index ea5b85354526..24bacdb315c6 100644
@@ -562,7 +562,8 @@ static void devlink_remove_symlinks(struct device *dev,
 	struct device *con = link->consumer;
 	char *buf;
 
-	sysfs_remove_link(&link->link_dev.kobj, "consumer");
+	if (device_is_registered(con))
+		sysfs_remove_link(&link->link_dev.kobj, "consumer");
 	sysfs_remove_link(&link->link_dev.kobj, "supplier");
 
 	len = max(strlen(dev_bus_name(sup)) + strlen(dev_name(sup)),

@@ -575,8 +576,10 @@ static void devlink_remove_symlinks(struct device *dev,
 		return;
 	}
 
-	snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
-	sysfs_remove_link(&con->kobj, buf);
+	if (device_is_registered(con)) {
+		snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
+		sysfs_remove_link(&con->kobj, buf);
+	}
 	snprintf(buf, len, "consumer:%s:%s", dev_bus_name(con), dev_name(con));
 	sysfs_remove_link(&sup->kobj, buf);
 	kfree(buf);

@@ -885,6 +888,8 @@ 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");
 }

Signature · 1 line

2.17.1

Greg Kroah-Hartman

maintainer

2021-07-09 09:55 UTC #2 lore raw

Quoted 6 lines · Adrian Hunter

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 discover 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.

Why are you not just manually removing the link you just created? You manually added it, you know something failed so you need to clean up, so why not clean this up too?

thanks,

greg k-h

Rafael J. Wysocki

maintainer

2021-07-09 11:19 UTC #3 lore raw

Quoted 9 lines · Greg Kroah-Hartman

Quoted 6 lines · Adrian Hunter
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 discover 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.

Quoted 3 lines

Why are you not just manually removing the link you just created? You manually added it, you know something failed so you need to clean up, so why not clean this up too?

His changes are needed to do just that.

Rafael J. Wysocki

maintainer

2021-07-09 11:29 UTC #4 lore raw

In reply to Adrian Hunter

Quoted 27 lines · Adrian Hunter

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 discover 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.
Amend device link removal to accept removal of a link with an unregistered consumer device.
To make that work nicely, the devlink_remove_symlinks() function must be amended to cope with the absence of the consumer's sysfs presence, otherwise sysfs_remove_link() will generate a warning.
Suggested-by Rafael J. Wysocki <[email protected]>
Fixes b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")
Signed-off-by Adrian Hunter <[email protected]>
---
 drivers/base/core.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
drivers/base/core.c +0 -0
index ea5b85354526..24bacdb315c6 100644

drivers/base/core.c static void devlink_remove_symlinks(struct device *dev, · line 566

Quoted 6 lines

drivers/base/core.c +2 -1

@@ -562,7 +562,8 @@ static void devlink_remove_symlinks(struct device *dev,
        struct device *con = link->consumer;
        char *buf;
 
-       sysfs_remove_link(&link->link_dev.kobj, "consumer");
+       if (device_is_registered(con))
+               sysfs_remove_link(&link->link_dev.kobj, "consumer");

I think that this is needed regardless of the changes in device_link_put_kref(), because if somebody decides to delete a stateless device link before registering the consumer device, sysfs_remove_link() will still complain, won't it?

drivers/base/core.c static void devlink_remove_symlinks(struct device *dev, · line 582

Quoted 13 lines

drivers/base/core.c +4 -2

        sysfs_remove_link(&link->link_dev.kobj, "supplier");
 
        len = max(strlen(dev_bus_name(sup)) + strlen(dev_name(sup)),

@@ -575,8 +576,10 @@ static void devlink_remove_symlinks(struct device *dev,
                return;
        }
 
-       snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
-       sysfs_remove_link(&con->kobj, buf);
+       if (device_is_registered(con)) {
+               snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
+               sysfs_remove_link(&con->kobj, buf);
+       }

And here too, if I'm not mistaken.

So in that case it would be better to put the above changes into a separate patch and add a Fixes tag to it.

Quoted 15 lines

drivers/base/core.c +2 -1

        snprintf(buf, len, "consumer:%s:%s", dev_bus_name(con), dev_name(con));
        sysfs_remove_link(&sup->kobj, buf);
        kfree(buf);

@@ -885,6 +888,8 @@ 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");
 }
--

2.17.1

Adrian Hunter

author

2021-07-09 13:18 UTC #5 lore raw

Quoted 31 lines · Rafael J. Wysocki

Quoted 30 lines · Adrian Hunter
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 discover 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.
Amend device link removal to accept removal of a link with an unregistered consumer device.
To make that work nicely, the devlink_remove_symlinks() function must be amended to cope with the absence of the consumer's sysfs presence, otherwise sysfs_remove_link() will generate a warning.
Suggested-by Rafael J. Wysocki <[email protected]>
Fixes b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")
Signed-off-by Adrian Hunter <[email protected]>
---
 drivers/base/core.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
drivers/base/core.c +0 -0
index ea5b85354526..24bacdb315c6 100644
@@ -562,7 +562,8 @@ static void devlink_remove_symlinks(struct device *dev,
        struct device *con = link->consumer;
        char *buf;
 

Quoted 8 lines

drivers/base/core.c static void devlink_remove_symlinks(struct device *dev, · line 566
Quoted 3 lines
drivers/base/core.c +2 -1
-       sysfs_remove_link(&link->link_dev.kobj, "consumer");
+       if (device_is_registered(con))
+               sysfs_remove_link(&link->link_dev.kobj, "consumer");
I think that this is needed regardless of the changes in device_link_put_kref(), because if somebody decides to delete a stateless device link before registering the consumer device, sysfs_remove_link() will still complain, won't it?

I would think so.

Quoted 17 lines

Quoted 5 lines

drivers/base/core.c +0 -0

        sysfs_remove_link(&link->link_dev.kobj, "supplier");
 
        len = max(strlen(dev_bus_name(sup)) + strlen(dev_name(sup)),

drivers/base/core.c static void devlink_remove_symlinks(struct device *dev, · line 582

Quoted 9 lines

drivers/base/core.c +4 -2

@@ -575,8 +576,10 @@ static void devlink_remove_symlinks(struct device *dev,
                return;
        }
 
-       snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
-       sysfs_remove_link(&con->kobj, buf);
+       if (device_is_registered(con)) {
+               snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
+               sysfs_remove_link(&con->kobj, buf);
+       }

And here too, if I'm not mistaken.

Quoted 2 lines

So in that case it would be better to put the above changes into a separate patch and add a Fixes tag to it.

Yes, that makes sense. I'll send a V3

Quoted 16 lines

drivers/base/core.c +2 -1

        snprintf(buf, len, "consumer:%s:%s", dev_bus_name(con), dev_name(con));
        sysfs_remove_link(&sup->kobj, buf);
        kfree(buf);

@@ -885,6 +888,8 @@ 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");
 }
--

2.17.1

Adrian Hunter

author

2021-07-09 06:43 UTC #6 lore raw

PATCH v2 2/2 scsi: ufshcd: Fix device links when BOOT WLUN fails to probe

In reply to Adrian Hunter

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.

Fixes b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")

Signed-off-by Adrian Hunter <[email protected]>

---
 drivers/scsi/ufs/ufshcd.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

drivers/scsi/ufs/ufshcd.c +21 -2

index 708b3b62fc4d..9864a8ee0263 100644
@@ -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);
+		}
 	}
 }

Signature · 1 line

2.17.1