[PATCH] dax/bus.c: replace WARN_ON_ONCE() with lockdep asserts

[Vishal Verma]

In [1], Dan points out that all of the WARN_ON_ONCE() usage in the
referenced patch should be replaced with lockdep_assert_held(_write)().

Replace those, and additionally, replace a couple of other
WARN_ON_ONCE() introduced in the same patch for actual failure
cases (i.e. when acquiring a semaphore fails in a remove / unregister
path) with dev_WARN_ONCE() as is the precedent here.

Recall that previously, unregistration paths was implicitly protected by
overloading the device lock, which the patch in [1] sought to remove.
This meant adding a semaphore acquisition in these unregistration paths.
Since that can fail, and it doesn't make sense to return errors from
these paths, retain the two instances of (now) dev_WARN_ONCE().

Link: https://lore.kernel.org/r/65f0b5ef41817_aa222941a@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.notmuch [1]
Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
---
 drivers/dax/bus.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 797e1ebff299..d89c8c3b62f7 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -192,7 +192,7 @@ static u64 dev_dax_size(struct dev_dax *dev_dax)
 	u64 size = 0;
 	int i;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_dev_rwsem));
+	lockdep_assert_held(&dax_dev_rwsem);
 
 	for (i = 0; i < dev_dax->nr_range; i++)
 		size += range_len(&dev_dax->ranges[i].range);
@@ -302,7 +302,7 @@ static unsigned long long dax_region_avail_size(struct dax_region *dax_region)
 	resource_size_t size = resource_size(&dax_region->res);
 	struct resource *res;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held(&dax_region_rwsem);
 
 	for_each_dax_region_resource(dax_region, res)
 		size -= resource_size(res);
@@ -447,7 +447,7 @@ static void trim_dev_dax_range(struct dev_dax *dev_dax)
 	struct range *range = &dev_dax->ranges[i].range;
 	struct dax_region *dax_region = dev_dax->region;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held_write(&dax_region_rwsem);
 	dev_dbg(&dev_dax->dev, "delete range[%d]: %#llx:%#llx\n", i,
 		(unsigned long long)range->start,
 		(unsigned long long)range->end);
@@ -471,6 +471,7 @@ static void __unregister_dev_dax(void *dev)
 
 	dev_dbg(dev, "%s\n", __func__);
 
+	lockdep_assert_held_write(&dax_region_rwsem);
 	kill_dev_dax(dev_dax);
 	device_del(dev);
 	free_dev_dax_ranges(dev_dax);
@@ -482,7 +483,8 @@ 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))
+	if (dev_WARN_ONCE(dev, down_write_killable(&dax_region_rwsem) != 0,
+			  "unable to acquire region rwsem\n"))
 		return;
 	__unregister_dev_dax(dev);
 	up_write(&dax_region_rwsem);
@@ -507,7 +509,7 @@ static int __free_dev_dax_id(struct dev_dax *dev_dax)
 	struct dax_region *dax_region;
 	int rc = dev_dax->id;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_dev_rwsem));
+	lockdep_assert_held_write(&dax_dev_rwsem);
 
 	if (!dev_dax->dyn_id || dev_dax->id < 0)
 		return -1;
@@ -713,7 +715,7 @@ static void __unregister_dax_mapping(void *data)
 
 	dev_dbg(dev, "%s\n", __func__);
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held_write(&dax_region_rwsem);
 
 	dev_dax->ranges[mapping->range_id].mapping = NULL;
 	mapping->range_id = -1;
@@ -726,7 +728,8 @@ 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))
+	if (dev_WARN_ONCE(data, down_write_killable(&dax_region_rwsem) != 0,
+			  "unable to acquire region rwsem\n"))
 		return;
 	__unregister_dax_mapping(data);
 	up_write(&dax_region_rwsem);
@@ -830,7 +833,7 @@ static int devm_register_dax_mapping(struct dev_dax *dev_dax, int range_id)
 	struct device *dev;
 	int rc;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held_write(&dax_region_rwsem);
 
 	if (dev_WARN_ONCE(&dev_dax->dev, !dax_region->dev->driver,
 				"region disabled\n"))
@@ -876,7 +879,7 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
 	struct resource *alloc;
 	int i, rc;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held_write(&dax_region_rwsem);
 
 	/* handle the seed alloc special case */
 	if (!size) {
@@ -935,7 +938,7 @@ static int adjust_dev_dax_range(struct dev_dax *dev_dax, struct resource *res, r
 	struct device *dev = &dev_dax->dev;
 	int rc;
 
-	WARN_ON_ONCE(!rwsem_is_locked(&dax_region_rwsem));
+	lockdep_assert_held_write(&dax_region_rwsem);
 
 	if (dev_WARN_ONCE(dev, !size, "deletion is handled by dev_dax_shrink\n"))
 		return -EINVAL;

---
base-commit: 39cd87c4eb2b893354f3b850f916353f2658ae6f
change-id: 20240402-vv-dax_abi_fixes-8af3b6ff2e5a

Best regards,
-- 
Vishal Verma <vishal.l.verma@xxxxxxxxx>