bisecting fixing commit since a844dc4c544291470aa69edbe2434b040794e269
building syzkaller on 4b83c8fbed7b9cea831be880ec8aa1098b465f25
testing commit a844dc4c544291470aa69edbe2434b040794e269 with gcc (GCC) 8.1.0
kernel signature: 2690983520ca116f50caf35e0908959521b845e04181428fc04d111ab3f0a742
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
testing current HEAD 4520f06b03ae667e442da1ab9351fd28cd7ac598
testing commit 4520f06b03ae667e442da1ab9351fd28cd7ac598 with gcc (GCC) 8.1.0
kernel signature: 50c7c7bdcc2b50545db4d5bf0f89446798691dd17ee7f50f593f088819a540f8
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
revisions tested: 2, total time: 23m20.329977982s (build: 16m49.572259374s, test: 5m52.341656606s)
the crash still happens on HEAD
commit msg: Linux 4.14.175
crash: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
IPv6: ADDRCONF(NETDEV_UP): veth0_to_hsr: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_bond: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_team: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): team_slave_0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_team: link becomes ready
BUG: unable to handle kernel NULL pointer dereference at 0000000000000003
IPv6: ADDRCONF(NETDEV_CHANGE): team_slave_1: link becomes ready
IP: writeb arch/x86/include/asm/io.h:65 [inline]
IP: mem_serial_out+0x61/0x90 drivers/tty/serial/8250/8250_port.c:408
PGD 8e3bd067 P4D 8e3bd067 PUD 8e3be067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 7308 Comm: syz-executor.2 Not tainted 4.14.175-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff888083d2c680 task.stack: ffff888083cf8000
RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline]
RIP: 0010:mem_serial_out+0x61/0x90 drivers/tty/serial/8250/8250_port.c:408
RSP: 0018:ffff888083cff8c0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff8a45edd0 RCX: 1ffffffff148bdc2
RDX: 00000000000000bf RSI: 0000000000000003 RDI: ffffffff8a45ee10
RBP: ffff888083cff8d0 R08: ffff888083d2cf48 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8a45ef10
R13: ffffffff8a45edd0 R14: ffffffff8a45ee20 R15: ffffffff8a45ee9c
FS:  00007f82caa39700(0000) GS:ffff8880aed00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000003 CR3: 000000008e3bc000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 serial_port_out include/linux/serial_core.h:266 [inline]
 serial8250_do_startup+0xd7f/0x1b10 drivers/tty/serial/8250/8250_port.c:2140
 serial8250_startup+0x39/0x50 drivers/tty/serial/8250/8250_port.c:2415
 uart_port_startup drivers/tty/serial/serial_core.c:231 [inline]
 uart_startup.part.20+0x2a0/0x710 drivers/tty/serial/serial_core.c:270
 uart_startup drivers/tty/serial/serial_core.c:267 [inline]
 uart_set_info drivers/tty/serial/serial_core.c:1010 [inline]
 uart_set_info_user drivers/tty/serial/serial_core.c:1038 [inline]
 uart_ioctl+0x127e/0x2b90 drivers/tty/serial/serial_core.c:1361
 tty_ioctl+0x434/0x1260 drivers/tty/tty_io.c:2661
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_hsr: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): hsr_slave_0: link becomes ready
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684
IPv6: ADDRCONF(NETDEV_UP): veth0_to_team: link is not ready
IPv6: ADDRCONF(NETDEV_UP): veth1_to_team: link is not ready
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x74/0x80 fs/ioctl.c:692
IPv6: ADDRCONF(NETDEV_UP): veth0_to_hsr: link is not ready
 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45a6f9
IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready
RSP: 002b:00007f82caa38c78 EFLAGS: 00000246
hsr0: Slave A (hsr_slave_0) is not up; please bring it up to get a fully working HSR network
 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a6f9
RDX: 0000000020000080 RSI: 000000000000541f RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82caa396d4
R13: 00000000004c5c0b R14: 00000000004dbf70 R15: 00000000ffffffff
Code: 0f b6 8b d1 00 00 
hsr0: Slave B (hsr_slave_1) is not up; please bring it up to get a fully working HSR network
00 48 8d 7b 40 48 b8 00 00 00 00 00 fc ff df d3 e6 
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not ready
48 89 f9 48 c1 e9 03 80 3c 01 00 75 23 48 63 f6 48 
IPv6: ADDRCONF(NETDEV_UP): vxcan0: link is not ready
03 
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
73 
8021q: adding VLAN 0 to HW filter on device batadv0
40 <88> 16 48 83 c4 08 5b 5d c3 89 55 f0 89 75 f4 e8 2b c8 37 fe 8b 
RIP: writeb arch/x86/include/asm/io.h:65 [inline] RSP: ffff888083cff8c0
RIP: mem_serial_out+0x61/0x90 drivers/tty/serial/8250/8250_port.c:408 RSP: ffff888083cff8c0
CR2: 0000000000000003
IPv6: ADDRCONF(NETDEV_UP): veth1_to_team: link is not ready
---[ end trace 1c720b05bd2a5e1e ]---
IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready