f2fs: fix to do sanity check with cp_pack_start_sum

After fuzzing, cp_pack_start_sum could be corrupted, so current log's
summary info should be wrong due to loading incorrect summary block.
Then, if segment's type in current log is exceeded NR_CURSEG_TYPE, it
can lead accessing invalid dirty_i->dirty_segmap bitmap finally.

Add sanity check for cp_pack_start_sum to fix this issue.

https://bugzilla.kernel.org/show_bug.cgi?id=200419

- Reproduce

- Kernel message (f2fs-dev w/ KASAN)
[ 3117.578432] F2FS-fs (loop0): Invalid log blocks per segment (8)

[ 3117.578445] F2FS-fs (loop0): Can't find valid F2FS filesystem in 2th superblock
[ 3117.581364] F2FS-fs (loop0): invalid crc_offset: 30716
[ 3117.583564] WARNING: CPU: 1 PID: 1225 at fs/f2fs/checkpoint.c:90 __get_meta_page+0x448/0x4b0
[ 3117.583570] Modules linked in: snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_timer joydev input_leds serio_raw snd soundcore mac_hid i2c_piix4 ib_iser rdma_cm iw_cm ib_cm ib_core configfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi btrfs zstd_decompress zstd_compress xxhash raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear 8139too qxl ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcbc aesni_intel psmouse aes_x86_64 8139cp crypto_simd cryptd mii glue_helper pata_acpi floppy
[ 3117.584014] CPU: 1 PID: 1225 Comm: mount Not tainted 4.17.0+ #1
[ 3117.584017] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 3117.584022] RIP: 0010:__get_meta_page+0x448/0x4b0
[ 3117.584023] Code: 00 49 8d bc 24 84 00 00 00 e8 74 54 da ff 41 83 8c 24 84 00 00 00 08 4c 89 f6 4c 89 ef e8 c0 d9 95 00 48 89 ef e8 18 e3 00 00 <0f> 0b f0 80 4d 48 04 e9 0f fe ff ff 0f 0b 48 89 c7 48 89 04 24 e8
[ 3117.584072] RSP: 0018:ffff88018eb678c0 EFLAGS: 00010286
[ 3117.584082] RAX: ffff88018f0a6a78 RBX: ffffea0007a46600 RCX: ffffffff9314d1b2
[ 3117.584085] RDX: ffffffff00000001 RSI: 0000000000000000 RDI: ffff88018f0a6a98
[ 3117.584087] RBP: ffff88018ebe9980 R08: 0000000000000002 R09: 0000000000000001
[ 3117.584090] R10: 0000000000000001 R11: ffffed00326e4450 R12: ffff880193722200
[ 3117.584092] R13: ffff88018ebe9afc R14: 0000000000000206 R15: ffff88018eb67900
[ 3117.584096] FS:  00007f5694636840(0000) GS:ffff8801f3b00000(0000) knlGS:0000000000000000
[ 3117.584098] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3117.584101] CR2: 00000000016f21b8 CR3: 0000000191c22000 CR4: 00000000000006e0
[ 3117.584112] Call Trace:
[ 3117.584121]  ? f2fs_set_meta_page_dirty+0x150/0x150
[ 3117.584127]  ? f2fs_build_segment_manager+0xbf9/0x3190
[ 3117.584133]  ? f2fs_npages_for_summary_flush+0x75/0x120
[ 3117.584145]  f2fs_build_segment_manager+0xda8/0x3190
[ 3117.584151]  ? f2fs_get_valid_checkpoint+0x298/0xa00
[ 3117.584156]  ? f2fs_flush_sit_entries+0x10e0/0x10e0
[ 3117.584184]  ? map_id_range_down+0x17c/0x1b0
[ 3117.584188]  ? __put_user_ns+0x30/0x30
[ 3117.584206]  ? find_next_bit+0x53/0x90
[ 3117.584237]  ? cpumask_next+0x16/0x20
[ 3117.584249]  f2fs_fill_super+0x1948/0x2b40
[ 3117.584258]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.584279]  ? sget_userns+0x65e/0x690
[ 3117.584296]  ? set_blocksize+0x88/0x130
[ 3117.584302]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.584305]  mount_bdev+0x1c0/0x200
[ 3117.584310]  mount_fs+0x5c/0x190
[ 3117.584320]  vfs_kern_mount+0x64/0x190
[ 3117.584330]  do_mount+0x2e4/0x1450
[ 3117.584343]  ? lockref_put_return+0x130/0x130
[ 3117.584347]  ? copy_mount_string+0x20/0x20
[ 3117.584357]  ? kasan_unpoison_shadow+0x31/0x40
[ 3117.584362]  ? kasan_kmalloc+0xa6/0xd0
[ 3117.584373]  ? memcg_kmem_put_cache+0x16/0x90
[ 3117.584377]  ? __kmalloc_track_caller+0x196/0x210
[ 3117.584383]  ? _copy_from_user+0x61/0x90
[ 3117.584396]  ? memdup_user+0x3e/0x60
[ 3117.584401]  ksys_mount+0x7e/0xd0
[ 3117.584405]  __x64_sys_mount+0x62/0x70
[ 3117.584427]  do_syscall_64+0x73/0x160
[ 3117.584440]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 3117.584455] RIP: 0033:0x7f5693f14b9a
[ 3117.584456] Code: 48 8b 0d 01 c3 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ce c2 2b 00 f7 d8 64 89 01 48
[ 3117.584505] RSP: 002b:00007fff27346488 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[ 3117.584510] RAX: ffffffffffffffda RBX: 00000000016e2030 RCX: 00007f5693f14b9a
[ 3117.584512] RDX: 00000000016e2210 RSI: 00000000016e3f30 RDI: 00000000016ee040
[ 3117.584514] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000013
[ 3117.584516] R10: 00000000c0ed0000 R11: 0000000000000206 R12: 00000000016ee040
[ 3117.584519] R13: 00000000016e2210 R14: 0000000000000000 R15: 0000000000000003
[ 3117.584523] ---[ end trace a8e0d899985faf31 ]---
[ 3117.685663] F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=2, run fsck to fix.
[ 3117.685673] F2FS-fs (loop0): recover_data: ino = 2 (i_size: recover) recovered = 1, err = 0
[ 3117.685707] ==================================================================
[ 3117.685955] BUG: KASAN: slab-out-of-bounds in __remove_dirty_segment+0xdd/0x1e0
[ 3117.686175] Read of size 8 at addr ffff88018f0a63d0 by task mount/1225

[ 3117.686477] CPU: 0 PID: 1225 Comm: mount Tainted: G        W         4.17.0+ #1
[ 3117.686481] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 3117.686483] Call Trace:
[ 3117.686494]  dump_stack+0x71/0xab
[ 3117.686512]  print_address_description+0x6b/0x290
[ 3117.686517]  kasan_report+0x28e/0x390
[ 3117.686522]  ? __remove_dirty_segment+0xdd/0x1e0
[ 3117.686527]  __remove_dirty_segment+0xdd/0x1e0
[ 3117.686532]  locate_dirty_segment+0x189/0x190
[ 3117.686538]  f2fs_allocate_new_segments+0xa9/0xe0
[ 3117.686543]  recover_data+0x703/0x2c20
[ 3117.686547]  ? f2fs_recover_fsync_data+0x48f/0xd50
[ 3117.686553]  ? ksys_mount+0x7e/0xd0
[ 3117.686564]  ? policy_nodemask+0x1a/0x90
[ 3117.686567]  ? policy_node+0x56/0x70
[ 3117.686571]  ? add_fsync_inode+0xf0/0xf0
[ 3117.686592]  ? blk_finish_plug+0x44/0x60
[ 3117.686597]  ? f2fs_ra_meta_pages+0x38b/0x5e0
[ 3117.686602]  ? find_inode_fast+0xac/0xc0
[ 3117.686606]  ? f2fs_is_valid_blkaddr+0x320/0x320
[ 3117.686618]  ? __radix_tree_lookup+0x150/0x150
[ 3117.686633]  ? dqget+0x670/0x670
[ 3117.686648]  ? pagecache_get_page+0x29/0x410
[ 3117.686656]  ? kmem_cache_alloc+0x176/0x1e0
[ 3117.686660]  ? f2fs_is_valid_blkaddr+0x11d/0x320
[ 3117.686664]  f2fs_recover_fsync_data+0xc23/0xd50
[ 3117.686670]  ? f2fs_space_for_roll_forward+0x60/0x60
[ 3117.686674]  ? rb_insert_color+0x323/0x3d0
[ 3117.686678]  ? f2fs_recover_orphan_inodes+0xa5/0x700
[ 3117.686683]  ? proc_register+0x153/0x1d0
[ 3117.686686]  ? f2fs_remove_orphan_inode+0x10/0x10
[ 3117.686695]  ? f2fs_attr_store+0x50/0x50
[ 3117.686700]  ? proc_create_single_data+0x52/0x60
[ 3117.686707]  f2fs_fill_super+0x1d06/0x2b40
[ 3117.686728]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.686735]  ? sget_userns+0x65e/0x690
[ 3117.686740]  ? set_blocksize+0x88/0x130
[ 3117.686745]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.686748]  mount_bdev+0x1c0/0x200
[ 3117.686753]  mount_fs+0x5c/0x190
[ 3117.686758]  vfs_kern_mount+0x64/0x190
[ 3117.686762]  do_mount+0x2e4/0x1450
[ 3117.686769]  ? lockref_put_return+0x130/0x130
[ 3117.686773]  ? copy_mount_string+0x20/0x20
[ 3117.686777]  ? kasan_unpoison_shadow+0x31/0x40
[ 3117.686780]  ? kasan_kmalloc+0xa6/0xd0
[ 3117.686786]  ? memcg_kmem_put_cache+0x16/0x90
[ 3117.686790]  ? __kmalloc_track_caller+0x196/0x210
[ 3117.686795]  ? _copy_from_user+0x61/0x90
[ 3117.686801]  ? memdup_user+0x3e/0x60
[ 3117.686804]  ksys_mount+0x7e/0xd0
[ 3117.686809]  __x64_sys_mount+0x62/0x70
[ 3117.686816]  do_syscall_64+0x73/0x160
[ 3117.686824]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 3117.686829] RIP: 0033:0x7f5693f14b9a
[ 3117.686830] Code: 48 8b 0d 01 c3 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ce c2 2b 00 f7 d8 64 89 01 48
[ 3117.686887] RSP: 002b:00007fff27346488 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[ 3117.686892] RAX: ffffffffffffffda RBX: 00000000016e2030 RCX: 00007f5693f14b9a
[ 3117.686894] RDX: 00000000016e2210 RSI: 00000000016e3f30 RDI: 00000000016ee040
[ 3117.686896] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000013
[ 3117.686899] R10: 00000000c0ed0000 R11: 0000000000000206 R12: 00000000016ee040
[ 3117.686901] R13: 00000000016e2210 R14: 0000000000000000 R15: 0000000000000003

[ 3117.687005] Allocated by task 1225:
[ 3117.687152]  kasan_kmalloc+0xa6/0xd0
[ 3117.687157]  kmem_cache_alloc_trace+0xfd/0x200
[ 3117.687161]  f2fs_build_segment_manager+0x2d09/0x3190
[ 3117.687165]  f2fs_fill_super+0x1948/0x2b40
[ 3117.687168]  mount_bdev+0x1c0/0x200
[ 3117.687171]  mount_fs+0x5c/0x190
[ 3117.687174]  vfs_kern_mount+0x64/0x190
[ 3117.687177]  do_mount+0x2e4/0x1450
[ 3117.687180]  ksys_mount+0x7e/0xd0
[ 3117.687182]  __x64_sys_mount+0x62/0x70
[ 3117.687186]  do_syscall_64+0x73/0x160
[ 3117.687190]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

[ 3117.687285] Freed by task 19:
[ 3117.687412]  __kasan_slab_free+0x137/0x190
[ 3117.687416]  kfree+0x8b/0x1b0
[ 3117.687460]  ttm_bo_man_put_node+0x61/0x80 [ttm]
[ 3117.687476]  ttm_bo_cleanup_refs+0x15f/0x250 [ttm]
[ 3117.687492]  ttm_bo_delayed_delete+0x2f0/0x300 [ttm]
[ 3117.687507]  ttm_bo_delayed_workqueue+0x17/0x50 [ttm]
[ 3117.687528]  process_one_work+0x2f9/0x740
[ 3117.687531]  worker_thread+0x78/0x6b0
[ 3117.687541]  kthread+0x177/0x1c0
[ 3117.687545]  ret_from_fork+0x35/0x40

[ 3117.687638] The buggy address belongs to the object at ffff88018f0a6300
                which belongs to the cache kmalloc-192 of size 192
[ 3117.688014] The buggy address is located 16 bytes to the right of
                192-byte region [ffff88018f0a6300, ffff88018f0a63c0)
[ 3117.688382] The buggy address belongs to the page:
[ 3117.688554] page:ffffea00063c2980 count:1 mapcount:0 mapping:ffff8801f3403180 index:0x0
[ 3117.688788] flags: 0x17fff8000000100(slab)
[ 3117.688944] raw: 017fff8000000100 ffffea00063c2840 0000000e0000000e ffff8801f3403180
[ 3117.689166] raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
[ 3117.689386] page dumped because: kasan: bad access detected

[ 3117.689653] Memory state around the buggy address:
[ 3117.689816]  ffff88018f0a6280: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[ 3117.690027]  ffff88018f0a6300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 3117.690239] >ffff88018f0a6380: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3117.690448]                                                  ^
[ 3117.690644]  ffff88018f0a6400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 3117.690868]  ffff88018f0a6480: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 3117.691077] ==================================================================
[ 3117.691290] Disabling lock debugging due to kernel taint
[ 3117.693893] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[ 3117.694120] PGD 80000001f01bc067 P4D 80000001f01bc067 PUD 1d9638067 PMD 0
[ 3117.694338] Oops: 0002 [#1] SMP KASAN PTI
[ 3117.694490] CPU: 1 PID: 1225 Comm: mount Tainted: G    B   W         4.17.0+ #1
[ 3117.694703] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 3117.695073] RIP: 0010:__remove_dirty_segment+0xe2/0x1e0
[ 3117.695246] Code: c4 48 89 c7 e8 cf bb d7 ff 45 0f b6 24 24 41 83 e4 3f 44 88 64 24 07 41 83 e4 3f 4a 8d 7c e3 08 e8 b3 bc d7 ff 4a 8b 4c e3 08 <f0> 4c 0f b3 29 0f 82 94 00 00 00 48 8d bd 20 04 00 00 e8 97 bb d7
[ 3117.695793] RSP: 0018:ffff88018eb67638 EFLAGS: 00010292
[ 3117.695969] RAX: 0000000000000000 RBX: ffff88018f0a6300 RCX: 0000000000000000
[ 3117.696182] RDX: 0000000000000000 RSI: 0000000000000297 RDI: 0000000000000297
[ 3117.696391] RBP: ffff88018ebe9980 R08: ffffed003e743ebb R09: ffffed003e743ebb
[ 3117.696604] R10: 0000000000000001 R11: ffffed003e743eba R12: 0000000000000019
[ 3117.696813] R13: 0000000000000014 R14: 0000000000000320 R15: ffff88018ebe99e0
[ 3117.697032] FS:  00007f5694636840(0000) GS:ffff8801f3b00000(0000) knlGS:0000000000000000
[ 3117.697280] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3117.702357] CR2: 00007fe89bb1a000 CR3: 0000000191c22000 CR4: 00000000000006e0
[ 3117.707235] Call Trace:
[ 3117.712077]  locate_dirty_segment+0x189/0x190
[ 3117.716891]  f2fs_allocate_new_segments+0xa9/0xe0
[ 3117.721617]  recover_data+0x703/0x2c20
[ 3117.726316]  ? f2fs_recover_fsync_data+0x48f/0xd50
[ 3117.730957]  ? ksys_mount+0x7e/0xd0
[ 3117.735573]  ? policy_nodemask+0x1a/0x90
[ 3117.740198]  ? policy_node+0x56/0x70
[ 3117.744829]  ? add_fsync_inode+0xf0/0xf0
[ 3117.749487]  ? blk_finish_plug+0x44/0x60
[ 3117.754152]  ? f2fs_ra_meta_pages+0x38b/0x5e0
[ 3117.758831]  ? find_inode_fast+0xac/0xc0
[ 3117.763448]  ? f2fs_is_valid_blkaddr+0x320/0x320
[ 3117.768046]  ? __radix_tree_lookup+0x150/0x150
[ 3117.772603]  ? dqget+0x670/0x670
[ 3117.777159]  ? pagecache_get_page+0x29/0x410
[ 3117.781648]  ? kmem_cache_alloc+0x176/0x1e0
[ 3117.786067]  ? f2fs_is_valid_blkaddr+0x11d/0x320
[ 3117.790476]  f2fs_recover_fsync_data+0xc23/0xd50
[ 3117.794790]  ? f2fs_space_for_roll_forward+0x60/0x60
[ 3117.799086]  ? rb_insert_color+0x323/0x3d0
[ 3117.803304]  ? f2fs_recover_orphan_inodes+0xa5/0x700
[ 3117.807563]  ? proc_register+0x153/0x1d0
[ 3117.811766]  ? f2fs_remove_orphan_inode+0x10/0x10
[ 3117.815947]  ? f2fs_attr_store+0x50/0x50
[ 3117.820087]  ? proc_create_single_data+0x52/0x60
[ 3117.824262]  f2fs_fill_super+0x1d06/0x2b40
[ 3117.828367]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.832432]  ? sget_userns+0x65e/0x690
[ 3117.836500]  ? set_blocksize+0x88/0x130
[ 3117.840501]  ? f2fs_commit_super+0x1a0/0x1a0
[ 3117.844420]  mount_bdev+0x1c0/0x200
[ 3117.848275]  mount_fs+0x5c/0x190
[ 3117.852053]  vfs_kern_mount+0x64/0x190
[ 3117.855810]  do_mount+0x2e4/0x1450
[ 3117.859441]  ? lockref_put_return+0x130/0x130
[ 3117.862996]  ? copy_mount_string+0x20/0x20
[ 3117.866417]  ? kasan_unpoison_shadow+0x31/0x40
[ 3117.869719]  ? kasan_kmalloc+0xa6/0xd0
[ 3117.872948]  ? memcg_kmem_put_cache+0x16/0x90
[ 3117.876121]  ? __kmalloc_track_caller+0x196/0x210
[ 3117.879333]  ? _copy_from_user+0x61/0x90
[ 3117.882467]  ? memdup_user+0x3e/0x60
[ 3117.885604]  ksys_mount+0x7e/0xd0
[ 3117.888700]  __x64_sys_mount+0x62/0x70
[ 3117.891742]  do_syscall_64+0x73/0x160
[ 3117.894692]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 3117.897669] RIP: 0033:0x7f5693f14b9a
[ 3117.900563] Code: 48 8b 0d 01 c3 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ce c2 2b 00 f7 d8 64 89 01 48
[ 3117.906922] RSP: 002b:00007fff27346488 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[ 3117.910159] RAX: ffffffffffffffda RBX: 00000000016e2030 RCX: 00007f5693f14b9a
[ 3117.913469] RDX: 00000000016e2210 RSI: 00000000016e3f30 RDI: 00000000016ee040
[ 3117.916764] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000013
[ 3117.920071] R10: 00000000c0ed0000 R11: 0000000000000206 R12: 00000000016ee040
[ 3117.923393] R13: 00000000016e2210 R14: 0000000000000000 R15: 0000000000000003
[ 3117.926680] Modules linked in: snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_timer joydev input_leds serio_raw snd soundcore mac_hid i2c_piix4 ib_iser rdma_cm iw_cm ib_cm ib_core configfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi btrfs zstd_decompress zstd_compress xxhash raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear 8139too qxl ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcbc aesni_intel psmouse aes_x86_64 8139cp crypto_simd cryptd mii glue_helper pata_acpi floppy
[ 3117.949979] CR2: 0000000000000000
[ 3117.954283] ---[ end trace a8e0d899985faf32 ]---
[ 3117.958575] RIP: 0010:__remove_dirty_segment+0xe2/0x1e0
[ 3117.962810] Code: c4 48 89 c7 e8 cf bb d7 ff 45 0f b6 24 24 41 83 e4 3f 44 88 64 24 07 41 83 e4 3f 4a 8d 7c e3 08 e8 b3 bc d7 ff 4a 8b 4c e3 08 <f0> 4c 0f b3 29 0f 82 94 00 00 00 48 8d bd 20 04 00 00 e8 97 bb d7
[ 3117.971789] RSP: 0018:ffff88018eb67638 EFLAGS: 00010292
[ 3117.976333] RAX: 0000000000000000 RBX: ffff88018f0a6300 RCX: 0000000000000000
[ 3117.980926] RDX: 0000000000000000 RSI: 0000000000000297 RDI: 0000000000000297
[ 3117.985497] RBP: ffff88018ebe9980 R08: ffffed003e743ebb R09: ffffed003e743ebb
[ 3117.990098] R10: 0000000000000001 R11: ffffed003e743eba R12: 0000000000000019
[ 3117.994761] R13: 0000000000000014 R14: 0000000000000320 R15: ffff88018ebe99e0
[ 3117.999392] FS:  00007f5694636840(0000) GS:ffff8801f3b00000(0000) knlGS:0000000000000000
[ 3118.004096] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3118.008816] CR2: 00007fe89bb1a000 CR3: 0000000191c22000 CR4: 00000000000006e0

- Location
https://elixir.bootlin.com/linux/v4.18-rc3/source/fs/f2fs/segment.c#L775
		if (test_and_clear_bit(segno, dirty_i->dirty_segmap[t]))
			dirty_i->nr_dirty[t]--;
Here dirty_i->dirty_segmap[t] can be NULL which leads to crash in test_and_clear_bit()

Reported-by Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
