dax/bus.c: use the right locking mode (read vs write) in size_show

In size_show(), the dax_dev_rwsem only needs a read lock, but was
acquiring a write lock.  Change it to down_read_interruptible() so it
doesn't unnecessarily hold a write lock.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: c05ae9d ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Signed-off-by: Vishal Verma <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Cc: Alison Schofield <[email protected]>
Cc: Dave Jiang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: stellarhopper

drivers/dax/bus.c

@@ -937,11 +937,11 @@ static ssize_t size_show(struct device *dev,
 	unsigned long long size;
 	int rc;
 
-	rc = down_write_killable(&dax_dev_rwsem);
+	rc = down_read_interruptible(&dax_dev_rwsem);
 	if (rc)
 		return rc;
 	size = dev_dax_size(dev_dax);
-	up_write(&dax_dev_rwsem);
+	up_read(&dax_dev_rwsem);
 
 	return sysfs_emit(buf, "%llu\n", size);
 }