[PATCH v3 1/2] dax/bus: fix mapping attribute error reporting

[Muchun Song <songmuchun@bytedance.com>]

After the DAX configuration locking was converted to rwsems, successful
lock acquisition leaves rc set to zero in mapping_store(). Two error
paths can return this stale value: an unbound region driver and a
misaligned range size. The sysfs write therefore reports success without
allocating the requested range.

Return -ENXIO when the region driver is not bound and -EINVAL when the
range size is misaligned.

Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Assisted-by: LLM
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
---
v3:
- Collect Reviewed-by from Dave Jiang

v2:
- Return explicit errors before Device DAX range allocation
  (suggested by Dave Jiang)
- Move the patch before range alignment validation for independent
  backports (suggested by Dave Jiang)
---
 drivers/dax/bus.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index b809e1a264af..e40c25401cf0 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1192,7 +1192,7 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
 		return rc;
 	if (!dax_region->dev->driver) {
 		up_write(&dax_region_rwsem);
-		return rc;
+		return -ENXIO;
 	}
 	rc = down_write_killable(&dax_dev_rwsem);
 	if (rc) {
@@ -1201,8 +1201,12 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
 	}
 
 	to_alloc = range_len(&r);
-	if (alloc_is_aligned(dev_dax, to_alloc))
+	if (!alloc_is_aligned(dev_dax, to_alloc)) {
+		dev_dbg(dev, "%s: size: %zu misaligned\n", __func__, to_alloc);
+		rc = -EINVAL;
+	} else {
 		rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
+	}
 	up_write(&dax_dev_rwsem);
 	up_write(&dax_region_rwsem);
 
-- 
2.54.0