libnvdimm: fix nvdimm_bus_lock() vs device_lock() ordering

A debug patch to turn the standard device_lock() into something that
lockdep can analyze yielded the following:

 ======================================================
 [ INFO: possible circular locking dependency detected ]
 4.11.0-rc4+ #106 Tainted: G           O
 -------------------------------------------------------
 lt-libndctl/1898 is trying to acquire lock:
  (&dev->nvdimm_mutex/3){+.+.+.}, at: [<ffffffffc023c948>] nd_attach_ndns+0x178/0x1b0 [libnvdimm]

 but task is already holding lock:
  (&nvdimm_bus->reconfig_mutex){+.+.+.}, at: [<ffffffffc022e0b1>] nvdimm_bus_lock+0x21/0x30 [libnvdimm]

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #1 (&nvdimm_bus->reconfig_mutex){+.+.+.}:
        lock_acquire+0xf6/0x1f0
        __mutex_lock+0x88/0x980
        mutex_lock_nested+0x1b/0x20
        nvdimm_bus_lock+0x21/0x30 [libnvdimm]
        nvdimm_namespace_capacity+0x1b/0x40 [libnvdimm]
        nvdimm_namespace_common_probe+0x230/0x510 [libnvdimm]
        nd_pmem_probe+0x14/0x180 [nd_pmem]
        nvdimm_bus_probe+0xa9/0x260 [libnvdimm]

 -> #0 (&dev->nvdimm_mutex/3){+.+.+.}:
        __lock_acquire+0x1107/0x1280
        lock_acquire+0xf6/0x1f0
        __mutex_lock+0x88/0x980
        mutex_lock_nested+0x1b/0x20
        nd_attach_ndns+0x178/0x1b0 [libnvdimm]
        nd_namespace_store+0x308/0x3c0 [libnvdimm]
        namespace_store+0x87/0x220 [libnvdimm]

In this case '&dev->nvdimm_mutex/3' mirrors '&dev->mutex'.

Fix this by replacing the use of device_lock() with nvdimm_bus_lock() to protect
nd_{attach,detach}_ndns() operations.

Cc: <stable@vger.kernel.org>
Fixes: 8c2f7e86 ("libnvdimm: infrastructure for btt devices")
Reported-by: Yi Zhang <yizhan@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/btt_devs.c

@@ -314,7 +314,7 @@ int nd_btt_probe(struct device *dev, struct nd_namespace_common *ndns)
 	if (rc < 0) {
 		struct nd_btt *nd_btt = to_nd_btt(btt_dev);
 
-		__nd_detach_ndns(btt_dev, &nd_btt->ndns);
+		nd_detach_ndns(btt_dev, &nd_btt->ndns);
 		put_device(btt_dev);
 	}
 

drivers/nvdimm/claim.c

@@ -21,8 +21,13 @@
 void __nd_detach_ndns(struct device *dev, struct nd_namespace_common **_ndns)
 {
 	struct nd_namespace_common *ndns = *_ndns;
+	struct nvdimm_bus *nvdimm_bus;
 
-	lockdep_assert_held(&ndns->dev.mutex);
+	if (!ndns)
+		return;
+
+	nvdimm_bus = walk_to_nvdimm_bus(&ndns->dev);
+	lockdep_assert_held(&nvdimm_bus->reconfig_mutex);
 	dev_WARN_ONCE(dev, ndns->claim != dev, "%s: invalid claim\n", __func__);
 	ndns->claim = NULL;
 	*_ndns = NULL;
@@ -37,18 +42,20 @@ void nd_detach_ndns(struct device *dev,
 	if (!ndns)
 		return;
 	get_device(&ndns->dev);
-	device_lock(&ndns->dev);
+	nvdimm_bus_lock(&ndns->dev);
 	__nd_detach_ndns(dev, _ndns);
-	device_unlock(&ndns->dev);
+	nvdimm_bus_unlock(&ndns->dev);
 	put_device(&ndns->dev);
 }
 
 bool __nd_attach_ndns(struct device *dev, struct nd_namespace_common *attach,
 		struct nd_namespace_common **_ndns)
 {
+	struct nvdimm_bus *nvdimm_bus = walk_to_nvdimm_bus(&attach->dev);
+
 	if (attach->claim)
 		return false;
-	lockdep_assert_held(&attach->dev.mutex);
+	lockdep_assert_held(&nvdimm_bus->reconfig_mutex);
 	dev_WARN_ONCE(dev, *_ndns, "%s: invalid claim\n", __func__);
 	attach->claim = dev;
 	*_ndns = attach;
@@ -61,9 +68,9 @@ bool nd_attach_ndns(struct device *dev, struct nd_namespace_common *attach,
 {
 	bool claimed;
 
-	device_lock(&attach->dev);
+	nvdimm_bus_lock(&attach->dev);
 	claimed = __nd_attach_ndns(dev, attach, _ndns);
-	device_unlock(&attach->dev);
+	nvdimm_bus_unlock(&attach->dev);
 	return claimed;
 }
 
@@ -114,7 +121,7 @@ static void nd_detach_and_reset(struct device *dev,
 		struct nd_namespace_common **_ndns)
 {
 	/* detach the namespace and destroy / reset the device */
-	nd_detach_ndns(dev, _ndns);
+	__nd_detach_ndns(dev, _ndns);
 	if (is_idle(dev, *_ndns)) {
 		nd_device_unregister(dev, ND_ASYNC);
 	} else if (is_nd_btt(dev)) {
@@ -184,7 +191,7 @@ ssize_t nd_namespace_store(struct device *dev,
 	}
 
 	WARN_ON_ONCE(!is_nvdimm_bus_locked(dev));
-	if (!nd_attach_ndns(dev, ndns, _ndns)) {
+	if (!__nd_attach_ndns(dev, ndns, _ndns)) {
 		dev_dbg(dev, "%s already claimed\n",
 				dev_name(&ndns->dev));
 		len = -EBUSY;

drivers/nvdimm/dax_devs.c

@@ -124,7 +124,7 @@ int nd_dax_probe(struct device *dev, struct nd_namespace_common *ndns)
 	dev_dbg(dev, "%s: dax: %s\n", __func__,
 			rc == 0 ? dev_name(dax_dev) : "<none>");
 	if (rc < 0) {
-		__nd_detach_ndns(dax_dev, &nd_pfn->ndns);
+		nd_detach_ndns(dax_dev, &nd_pfn->ndns);
 		put_device(dax_dev);
 	} else
 		__nd_device_register(dax_dev);

drivers/nvdimm/pfn_devs.c

@@ -484,7 +484,7 @@ int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns)
 	dev_dbg(dev, "%s: pfn: %s\n", __func__,
 			rc == 0 ? dev_name(pfn_dev) : "<none>");
 	if (rc < 0) {
-		__nd_detach_ndns(pfn_dev, &nd_pfn->ndns);
+		nd_detach_ndns(pfn_dev, &nd_pfn->ndns);
 		put_device(pfn_dev);
 	} else
 		__nd_device_register(pfn_dev);