zonefs: Call page_address() on page acquired with GFP_KERNEL flag

zonefs_read_super() acquires a page with alloc_page(GFP_KERNEL). That
page cannot come from ZONE_HIGHMEM, thus there's no need to map it with
kmap().

Therefore, use a plain page_address() on that page.

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

fs/zonefs/super.c

@@ -1687,34 +1687,34 @@ static int zonefs_read_super(struct super_block *sb)
 	if (ret)
 		goto free_page;
 
-	super = kmap(page);
+	super = page_address(page);
 
 	ret = -EINVAL;
 	if (le32_to_cpu(super->s_magic) != ZONEFS_MAGIC)
-		goto unmap;
+		goto free_page;
 
 	stored_crc = le32_to_cpu(super->s_crc);
 	super->s_crc = 0;
 	crc = crc32(~0U, (unsigned char *)super, sizeof(struct zonefs_super));
 	if (crc != stored_crc) {
 		zonefs_err(sb, "Invalid checksum (Expected 0x%08x, got 0x%08x)",
 			   crc, stored_crc);
-		goto unmap;
+		goto free_page;
 	}
 
 	sbi->s_features = le64_to_cpu(super->s_features);
 	if (sbi->s_features & ~ZONEFS_F_DEFINED_FEATURES) {
 		zonefs_err(sb, "Unknown features set 0x%llx\n",
 			   sbi->s_features);
-		goto unmap;
+		goto free_page;
 	}
 
 	if (sbi->s_features & ZONEFS_F_UID) {
 		sbi->s_uid = make_kuid(current_user_ns(),
 				       le32_to_cpu(super->s_uid));
 		if (!uid_valid(sbi->s_uid)) {
 			zonefs_err(sb, "Invalid UID feature\n");
-			goto unmap;
+			goto free_page;
 		}
 	}
 
@@ -1723,7 +1723,7 @@ static int zonefs_read_super(struct super_block *sb)
 				       le32_to_cpu(super->s_gid));
 		if (!gid_valid(sbi->s_gid)) {
 			zonefs_err(sb, "Invalid GID feature\n");
-			goto unmap;
+			goto free_page;
 		}
 	}
 
@@ -1732,14 +1732,12 @@ static int zonefs_read_super(struct super_block *sb)
 
 	if (memchr_inv(super->s_reserved, 0, sizeof(super->s_reserved))) {
 		zonefs_err(sb, "Reserved area is being used\n");
-		goto unmap;
+		goto free_page;
 	}
 
 	import_uuid(&sbi->s_uuid, super->s_uuid);
 	ret = 0;
 
-unmap:
-	kunmap(page);
 free_page:
 	__free_page(page);