f2fs: fix to avoid panic in f2fs_remove_inode_page()

As Jungyeon reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=203219

- Overview
When mounting the attached crafted image and running program, I got this error.
Additionally, it hangs on sync after running the program.

The image is intentionally fuzzed from a normal f2fs image for testing and I enabled option CONFIG_F2FS_CHECK_FS on.

- Reproduces
cc poc_06.c
mkdir test
mount -t f2fs tmp.img test
cp a.out test
cd test
sudo ./a.out
sync

- Messages
 kernel BUG at fs/f2fs/node.c:1183!
 RIP: 0010:f2fs_remove_inode_page+0x294/0x2d0
 Call Trace:
  f2fs_evict_inode+0x2a3/0x3a0
  evict+0xba/0x180
  __dentry_kill+0xbe/0x160
  dentry_kill+0x46/0x180
  dput+0xbb/0x100
  do_renameat2+0x3c9/0x550
  __x64_sys_rename+0x17/0x20
  do_syscall_64+0x43/0xf0
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

The reason is f2fs_remove_inode_page() will trigger kernel panic due to
inconsistent i_blocks value of inode.

To avoid panic, let's just print debug message and set SBI_NEED_FSCK to
give a hint to fsck for latter repairing of potential image corruption.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
[Jaegeuk Kim: fix build warning and add unlikely]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -1179,8 +1179,14 @@ int f2fs_remove_inode_page(struct inode *inode)
 		f2fs_put_dnode(&dn);
 		return -EIO;
 	}
-	f2fs_bug_on(F2FS_I_SB(inode),
-			inode->i_blocks != 0 && inode->i_blocks != 8);
+
+	if (unlikely(inode->i_blocks != 0 && inode->i_blocks != 8)) {
+		f2fs_msg(F2FS_I_SB(inode)->sb, KERN_WARNING,
+			"Inconsistent i_blocks, ino:%lu, iblocks:%llu",
+			inode->i_ino,
+			(unsigned long long)inode->i_blocks);
+		set_sbi_flag(F2FS_I_SB(inode), SBI_NEED_FSCK);
+	}
 
 	/* will put inode & node pages */
 	err = truncate_node(&dn);