[PATCH 01/13] driver core, libnvdimm: disable manual unbind of dimms while region active

[Dan Williams]

There are scenarios where we need a middle ground between disabling all
manual bind/unbind attempts (via driver->suppress_bind_attrs) and
allowing unbind at any userspace-determined time.  Pinning modules takes
away one vector for unwanted out-of-sequence device_release_driver()
invocations, this new mechanism (via device->suppress_unbind_attr) takes
away another.

The first user of this mechanism is the libnvdimm sub-system where
manual dimm disabling should be prevented while the dimm is active in
any region.  Note that there is a 1:N dimm-to-region relationship which
is why this is implemented as a disable count rather than a flag.  This
forces userspace to disable regions before dimms when manually shutting
down a bus topology.

This does not affect any of the kernel-internal initiated invocations of
device_release_driver().

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/base/base.h             |    1 +
 drivers/base/bus.c              |   12 ++++++++++--
 drivers/base/core.c             |    1 +
 drivers/base/dd.c               |    2 +-
 drivers/nvdimm/namespace_devs.c |    1 +
 drivers/nvdimm/region_devs.c    |    4 +++-
 include/linux/device.h          |   20 ++++++++++++++++++++
 7 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index e05db388bd1c..129814b17ca6 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -109,6 +109,7 @@ extern int bus_add_driver(struct device_driver *drv);
 extern void bus_remove_driver(struct device_driver *drv);
 
 extern void driver_detach(struct device_driver *drv);
+extern void __device_release_driver(struct device *dev);
 extern int driver_probe_device(struct device_driver *drv, struct device *dev);
 extern void driver_deferred_probe_del(struct device *dev);
 static inline int driver_match_device(struct device_driver *drv,
diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 6470eb8088f4..b48a903f2d28 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -188,10 +188,18 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
 	if (dev && dev->driver == drv) {
 		if (dev->parent)	/* Needed for USB */
 			device_lock(dev->parent);
-		device_release_driver(dev);
+
+		device_lock(dev);
+		if (atomic_read(&dev->suppress_unbind_attr) > 0)
+			err = -EBUSY;
+		else {
+			__device_release_driver(dev);
+			err = count;
+		}
+		device_unlock(dev);
+
 		if (dev->parent)
 			device_unlock(dev->parent);
-		err = count;
 	}
 	put_device(dev);
 	bus_put(bus);
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 0a8bdade53f2..0ea0e8560e1d 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -708,6 +708,7 @@ void device_initialize(struct device *dev)
 	INIT_LIST_HEAD(&dev->devres_head);
 	device_pm_init(dev);
 	set_dev_node(dev, -1);
+	atomic_set(&dev->suppress_unbind_attr, 0);
 #ifdef CONFIG_GENERIC_MSI_IRQ
 	INIT_LIST_HEAD(&dev->msi_list);
 #endif
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 16688f50729c..9e21817ca2d6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -756,7 +756,7 @@ EXPORT_SYMBOL_GPL(driver_attach);
  * __device_release_driver() must be called with @dev lock held.
  * When called for a USB interface, @dev->parent lock must be held as well.
  */
-static void __device_release_driver(struct device *dev)
+void __device_release_driver(struct device *dev)
 {
 	struct device_driver *drv;
 
diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
index c5e3196c45b0..e65572b6092c 100644
--- a/drivers/nvdimm/namespace_devs.c
+++ b/drivers/nvdimm/namespace_devs.c
@@ -1950,6 +1950,7 @@ static int init_active_labels(struct nd_region *nd_region)
 		}
 		nd_mapping->ndd = ndd;
 		atomic_inc(&nvdimm->busy);
+		device_disable_unbind_attr(&nvdimm->dev);
 		get_ndd(ndd);
 
 		count = nd_label_active_count(ndd);
diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
index 40fcfea26fbb..320f0f3ea367 100644
--- a/drivers/nvdimm/region_devs.c
+++ b/drivers/nvdimm/region_devs.c
@@ -427,8 +427,10 @@ static void nd_region_notify_driver_action(struct nvdimm_bus *nvdimm_bus,
 			nd_mapping->labels = NULL;
 			put_ndd(ndd);
 			nd_mapping->ndd = NULL;
-			if (ndd)
+			if (ndd) {
 				atomic_dec(&nvdimm->busy);
+				device_enable_unbind_attr(&nvdimm->dev);
+			}
 		}
 
 		if (is_nd_pmem(dev))
diff --git a/include/linux/device.h b/include/linux/device.h
index 38f02814d53a..d9eaa85bb9cf 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -849,6 +849,7 @@ struct device {
 
 	void	(*release)(struct device *dev);
 	struct iommu_group	*iommu_group;
+	atomic_t		suppress_unbind_attr; /* disable manual unbind */
 
 	bool			offline_disabled:1;
 	bool			offline:1;
@@ -988,6 +989,25 @@ static inline void device_lock_assert(struct device *dev)
 	lockdep_assert_held(&dev->mutex);
 }
 
+static inline bool device_disable_unbind_attr(struct device *dev)
+{
+	bool suppressed = false;
+
+	device_lock(dev);
+	if (dev->driver) {
+		atomic_inc(&dev->suppress_unbind_attr);
+		suppressed = true;
+	}
+	device_unlock(dev);
+
+	return suppressed;
+}
+
+static inline bool device_enable_unbind_attr(struct device *dev)
+{
+	return atomic_dec_and_test(&dev->suppress_unbind_attr);
+}
+
 static inline struct device_node *dev_of_node(struct device *dev)
 {
 	if (!IS_ENABLED(CONFIG_OF))