[PATCH v2 2/4] dax/bus.c: fix locking for unregister_dax_dev / unregister_dax_mapping paths

[Vishal Verma <vishal.l.verma@xxxxxxxxx>]

Commit c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
was a bit overzealous in eliminating device_lock() usage, and ended up
removing a couple of lock acquisitions which were needed, and as a
result, fix some of the conditional locking missteps that the above
commit introduced in unregister_dax_dev() and unregister_dax_mapping().

Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
---
 drivers/dax/bus.c | 44 ++++++++++----------------------------------
 1 file changed, 10 insertions(+), 34 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 7924dd542a13..4e04b228b080 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -465,26 +465,17 @@ static void free_dev_dax_ranges(struct dev_dax *dev_dax)
 		trim_dev_dax_range(dev_dax);
 }
 
-static void __unregister_dev_dax(void *dev)
+static void unregister_dev_dax(void *dev)
 {
 	struct dev_dax *dev_dax = to_dev_dax(dev);
 
 	dev_dbg(dev, "%s\n", __func__);
 
+	down_write(&dax_region_rwsem);
 	kill_dev_dax(dev_dax);
 	device_del(dev);
 	free_dev_dax_ranges(dev_dax);
 	put_device(dev);
-}
-
-static void unregister_dev_dax(void *dev)
-{
-	if (rwsem_is_locked(&dax_region_rwsem))
-		return __unregister_dev_dax(dev);
-
-	if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
-		return;
-	__unregister_dev_dax(dev);
 	up_write(&dax_region_rwsem);
 }
 
@@ -560,15 +551,12 @@ static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
 	if (!victim)
 		return -ENXIO;
 
-	rc = down_write_killable(&dax_region_rwsem);
-	if (rc)
-		return rc;
-	rc = down_write_killable(&dax_dev_rwsem);
-	if (rc) {
-		up_write(&dax_region_rwsem);
-		return rc;
-	}
+	device_lock(dev);
+	device_lock(victim);
 	dev_dax = to_dev_dax(victim);
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc)
+		return rc;
 	if (victim->driver || dev_dax_size(dev_dax))
 		rc = -EBUSY;
 	else {
@@ -589,11 +577,12 @@ static ssize_t delete_store(struct device *dev, struct device_attribute *attr,
 			rc = -EBUSY;
 	}
 	up_write(&dax_dev_rwsem);
+	device_unlock(victim);
 
 	/* won the race to invalidate the device, clean it up */
 	if (do_del)
 		devm_release_action(dev, unregister_dev_dax, victim);
-	up_write(&dax_region_rwsem);
+	device_unlock(dev);
 	put_device(victim);
 
 	return rc;
@@ -705,7 +694,7 @@ static void dax_mapping_release(struct device *dev)
 	put_device(parent);
 }
 
-static void __unregister_dax_mapping(void *data)
+static void unregister_dax_mapping(void *data)
 {
 	struct device *dev = data;
 	struct dax_mapping *mapping = to_dax_mapping(dev);
@@ -713,25 +702,12 @@ static void __unregister_dax_mapping(void *data)
 
 	dev_dbg(dev, "%s\n", __func__);
 
-	lockdep_assert_held_write(&dax_region_rwsem);
-
 	dev_dax->ranges[mapping->range_id].mapping = NULL;
 	mapping->range_id = -1;
 
 	device_unregister(dev);
 }
 
-static void unregister_dax_mapping(void *data)
-{
-	if (rwsem_is_locked(&dax_region_rwsem))
-		return __unregister_dax_mapping(data);
-
-	if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
-		return;
-	__unregister_dax_mapping(data);
-	up_write(&dax_region_rwsem);
-}
-
 static struct dev_dax_range *get_dax_range(struct device *dev)
 {
 	struct dax_mapping *mapping = to_dax_mapping(dev);

-- 
2.44.0