ext4: check dioread_nolock on remount

commit 261cb20c upstream.

Currently we allow enabling dioread_nolock mount option on remount for
filesystems where blocksize < PAGE_CACHE_SIZE.  This isn't really
supported so fix the bug by moving the check for blocksize !=
PAGE_CACHE_SIZE into parse_options(). Change the original PAGE_SIZE to
PAGE_CACHE_SIZE along the way because that's what we are really
interested in.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/ext4/super.c

@@ -1942,6 +1942,16 @@ static int parse_options(char *options, struct super_block *sb,
 		}
 	}
 #endif
+	if (test_opt(sb, DIOREAD_NOLOCK)) {
+		int blocksize =
+			BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
+
+		if (blocksize < PAGE_CACHE_SIZE) {
+			ext4_msg(sb, KERN_ERR, "can't mount with "
+				 "dioread_nolock if block size != PAGE_SIZE");
+			return 0;
+		}
+	}
 	return 1;
 }
 
@@ -3367,15 +3377,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			clear_opt(sb, DELALLOC);
 	}
 
-	blocksize = BLOCK_SIZE << le32_to_cpu(es->s_log_block_size);
-	if (test_opt(sb, DIOREAD_NOLOCK)) {
-		if (blocksize < PAGE_SIZE) {
-			ext4_msg(sb, KERN_ERR, "can't mount with "
-				 "dioread_nolock if block size != PAGE_SIZE");
-			goto failed_mount;
-		}
-	}
-
 	sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
 		(test_opt(sb, POSIX_ACL) ? MS_POSIXACL : 0);
 
@@ -3417,6 +3418,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (!ext4_feature_set_ok(sb, (sb->s_flags & MS_RDONLY)))
 		goto failed_mount;
 
+	blocksize = BLOCK_SIZE << le32_to_cpu(es->s_log_block_size);
 	if (blocksize < EXT4_MIN_BLOCK_SIZE ||
 	    blocksize > EXT4_MAX_BLOCK_SIZE) {
 		ext4_msg(sb, KERN_ERR,