BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD a8e02067 P4D a8e02067 PUD 89f3b067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 31403 Comm: syz-executor.2 Not tainted 4.19.128-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:test_and_set_bit arch/x86/include/asm/bitops.h:209 [inline]
RIP: 0010:test_and_set_bit_lock arch/x86/include/asm/bitops.h:223 [inline]
RIP: 0010:trylock_buffer include/linux/buffer_head.h:367 [inline]
RIP: 0010:lock_buffer include/linux/buffer_head.h:373 [inline]
RIP: 0010:alloc_branch fs/minix/itree_common.c:88 [inline]
RIP: 0010:get_block+0x772/0x1320 fs/minix/itree_common.c:191
Code: 00 00 49 8b bc 24 28 01 00 00 b9 08 00 00 00 e8 a4 c5 bc ff 31 d2 be 74 01 00 00 48 c7 c7 60 3b 7c 87 49 89 c4 e8 8e 16 4e ff <f0> 49 0f ba 2c 24 02 40 0f 92 c6 31 ff 40 88 74 24 78 e8 d7 73 6f
RSP: 0018:ffff88803a427788 EFLAGS: 00010246
RAX: 0000000000000007 RBX: 0000000000000c98 RCX: 1ffffffff11f8958
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: ffff8880514b40e4
RBP: ffff88803a427920 R08: ffff8880514b40c0 R09: fffff940003a3adf
R10: fffff940003a3ade R11: ffffea0001d1d6f7 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff88803a42784c R15: ffff88803a427888
FS:  00007fe94899d700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000a8b0d000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 minix_get_block+0xe5/0x110 fs/minix/inode.c:379
 __block_write_begin_int+0x47d/0x1770 fs/buffer.c:1978
 __block_write_begin fs/buffer.c:2028 [inline]
 block_write_begin+0x58/0x2e0 fs/buffer.c:2087
 minix_write_begin+0x35/0xe0 fs/minix/inode.c:415
 generic_perform_write+0x1f8/0x4d0 mm/filemap.c:3162
 __generic_file_write_iter+0x24c/0x610 mm/filemap.c:3287
 generic_file_write_iter+0x3f4/0x725 mm/filemap.c:3315
 call_write_iter include/linux/fs.h:1821 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x512/0x760 fs/read_write.c:487
 vfs_write+0x1f3/0x540 fs/read_write.c:549
 ksys_write+0x12b/0x2a0 fs/read_write.c:599
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45ca59
Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe94899cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000050d7a0 RCX: 000000000045ca59
RDX: 0000000008800000 RSI: 0000000020000180 RDI: 0000000000000004
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000d15 R14: 00000000004cf6bb R15: 00007fe94899d6d4
Modules linked in:
CR2: 0000000000000000
ubi: mtd0 is already attached to ubi0
ubi: mtd0 is already attached to ubi0
---[ end trace 09a964dfad054280 ]---
RIP: 0010:test_and_set_bit arch/x86/include/asm/bitops.h:209 [inline]
RIP: 0010:test_and_set_bit_lock arch/x86/include/asm/bitops.h:223 [inline]
RIP: 0010:trylock_buffer include/linux/buffer_head.h:367 [inline]
RIP: 0010:lock_buffer include/linux/buffer_head.h:373 [inline]
RIP: 0010:alloc_branch fs/minix/itree_common.c:88 [inline]
RIP: 0010:get_block+0x772/0x1320 fs/minix/itree_common.c:191
Code: 00 00 49 8b bc 24 28 01 00 00 b9 08 00 00 00 e8 a4 c5 bc ff 31 d2 be 74 01 00 00 48 c7 c7 60 3b 7c 87 49 89 c4 e8 8e 16 4e ff <f0> 49 0f ba 2c 24 02 40 0f 92 c6 31 ff 40 88 74 24 78 e8 d7 73 6f
RSP: 0018:ffff88803a427788 EFLAGS: 00010246
RAX: 0000000000000007 RBX: 0000000000000c98 RCX: 1ffffffff11f8958
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: ffff8880514b40e4
RBP: ffff88803a427920 R08: ffff8880514b40c0 R09: fffff940003a3adf
R10: fffff940003a3ade R11: ffffea0001d1d6f7 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff88803a42784c R15: ffff88803a427888
FS:  00007fe94899d700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd1f643c000 CR3: 00000000a8b0d000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400