ext2: disallow setting xip on remount

Yan Zheng pointed out that ext2_remount lacks checking if -o xip should be
enabled or not. This patch checks for presence of direct_access on the
backing block device and if the blocksize meets the requirements.

Signed-off-by: Carsten Otte <[e-mail]>
Cc: Yan Zheng <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/ext2/super.c

···
 	sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
 		((sbi->s_mount_opt & EXT2_MOUNT_POSIX_ACL) ? MS_POSIXACL : 0);
 
+	ext2_xip_verify_sb(sb); /* see if bdev supports xip, unset
+				    EXT2_MOUNT_XIP if not */
+
+	if ((ext2_use_xip(sb)) && (sb->s_blocksize != PAGE_SIZE)) {
+		printk("XIP: Unsupported blocksize\n");
+		goto restore_opts;
+	}
+
 	es = sbi->s_es;
 	if (((sbi->s_mount_opt & EXT2_MOUNT_XIP) !=
 	    (old_mount_opt & EXT2_MOUNT_XIP)) &&