ext4: cleanup the dax handling in ext4_fill_super

Only call fs_dax_get_by_bdev once the sbi has been allocated and remove
the need for the dax_dev local variable.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-21-hch@lst.deSigned-off-by: NDan Williams <dan.j.williams@intel.com>

fs/ext4/super.c

@@ -3878,7 +3878,6 @@ static void ext4_setup_csum_trigger(struct super_block *sb,
 
 static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 {
-	struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
 	char *orig_data = kstrdup(data, GFP_KERNEL);
 	struct buffer_head *bh, **group_desc;
 	struct ext4_super_block *es = NULL;
@@ -3909,12 +3908,12 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if ((data && !orig_data) || !sbi)
 		goto out_free_base;
 
-	sbi->s_daxdev = dax_dev;
 	sbi->s_blockgroup_lock =
 		kzalloc(sizeof(struct blockgroup_lock), GFP_KERNEL);
 	if (!sbi->s_blockgroup_lock)
 		goto out_free_base;
 
+	sbi->s_daxdev = fs_dax_get_by_bdev(sb->s_bdev);
 	sb->s_fs_info = sbi;
 	sbi->s_sb = sb;
 	sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
@@ -4299,7 +4298,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto failed_mount;
 	}
 
-	if (dax_dev) {
+	if (sbi->s_daxdev) {
 		if (blocksize == PAGE_SIZE)
 			set_bit(EXT4_FLAGS_BDEV_IS_DAX, &sbi->s_ext4_flags);
 		else
@@ -5095,10 +5094,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 out_fail:
 	sb->s_fs_info = NULL;
 	kfree(sbi->s_blockgroup_lock);
+	fs_put_dax(sbi->s_daxdev);
 out_free_base:
 	kfree(sbi);
 	kfree(orig_data);
-	fs_put_dax(dax_dev);
 	return err ? err : ret;
 }