f2fs_sync_fs() -> write_checkpoint() calls stat_inc_cp_count(sbi->stat_info),
which needs stat_info allocation.
Otherwise, we can hit:

[254042.598623]  ? count_shadow_nodes+0xa0/0xa0
[254042.598633]  f2fs_sync_fs+0x65/0xd0 [f2fs]
[254042.598645]  f2fs_balance_fs_bg+0xe4/0x1c0 [f2fs]
[254042.598657]  f2fs_write_node_pages+0x34/0x1a0 [f2fs]
[254042.598664]  ? pagevec_lookup_entries+0x1e/0x30
[254042.598673]  do_writepages+0x1e/0x30
[254042.598682]  __writeback_single_inode+0x45/0x330
[254042.598688]  writeback_single_inode+0xd7/0x190
[254042.598694]  write_inode_now+0x86/0xa0
[254042.598699]  iput+0x122/0x200
[254042.598709]  f2fs_fill_super+0xd4a/0x14d0 [f2fs]
[254042.598717]  mount_bdev+0x184/0x1c0
[254042.598934]  ? f2fs_commit_super+0x100/0x100 [f2fs]
[254042.599142]  f2fs_mount+0x15/0x20 [f2fs]
[254042.599349]  mount_fs+0x39/0x160
[254042.599554]  ? __alloc_percpu+0x15/0x20
[254042.599759]  vfs_kern_mount+0x67/0x110
[254042.599972]  do_mount+0x1bb/0xc80
[254042.600175]  ? memdup_user+0x42/0x60
[254042.600380]  SyS_mount+0x83/0xd0
[254042.600583]  entry_SYSCALL_64_fastpath+0x1e/0xad
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>