bisecting fixing commit since a844dc4c544291470aa69edbe2434b040794e269
building syzkaller on 4b83c8fbed7b9cea831be880ec8aa1098b465f25
testing commit a844dc4c544291470aa69edbe2434b040794e269 with gcc (GCC) 8.1.0
kernel signature: 56a175433f149cd1adeca3f8b6eb0e21e12252ff34c8e898cbd0ae4779d68f65
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
testing current HEAD d71f695ce745df9544a85d8a762f16d72e72df00
testing commit d71f695ce745df9544a85d8a762f16d72e72df00 with gcc (GCC) 8.1.0
kernel signature: 650baf191ed61bfdf516eb2968de327d88a33c4137bb3f3566e3db0fde253a2f
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
revisions tested: 2, total time: 26m29.623099839s (build: 19m27.930307486s, test: 5m54.628495798s)
the crash still happens on HEAD
commit msg: Linux 4.14.179
crash: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
IPv6: ADDRCONF(NETDEV_UP): team_slave_1: link is not ready
team0: Port device team_slave_1 added
IPv6: ADDRCONF(NETDEV_UP): bridge_slave_0: link is not ready
IPv6: ADDRCONF(NETDEV_UP): bridge_slave_1: link is not ready
BUG: unable to handle kernel NULL pointer dereference at 0000000000000003
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 8e59d067 P4D 8e59d067 PUD 8f800067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 7321 Comm: syz-executor.5 Not tainted 4.14.179-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff888091a42100 task.stack: ffff888084580000
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:ffff8880845878c0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff8a460dd0 RCX: 1ffffffff148c1c2
RDX: 00000000000000bf RSI: 0000000000000003 RDI: ffffffff8a460e10
RBP: ffff8880845878d0 R08: ffff888091a429d0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8a460f10
R13: ffffffff8a460dd0 R14: ffffffff8a460e20 R15: ffffffff8a460e9c
FS:  00007f7352c85700(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000003 CR3: 000000008e493000 CR4: 00000000001406f0
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
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x180/0xfb0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x74/0x80 fs/ioctl.c:692
 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45a6f9
RSP: 002b:00007f7352c84c78 EFLAGS: 00000246 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: 00007f7352c856d4
R13: 00000000004c5c0b R14: 00000000004dbf70 R15: 00000000ffffffff
Code: 0f b6 8b d1 00 00 00 48 8d 7b 40 48 b8 00 00 00 00 00 fc ff df d3 e6 48 89 f9 48 c1 e9 03 80 3c 01 00 75 23 48 63 f6 48 03 73 40 <88> 16 48 83 c4 08 5b 5d c3 89 55 f0 89 75 f4 e8 0b a7 37 fe 8b 
RIP: writeb arch/x86/include/asm/io.h:65 [inline] RSP: ffff8880845878c0
RIP: mem_serial_out+0x61/0x90 drivers/tty/serial/8250/8250_port.c:408 RSP: ffff8880845878c0
CR2: 0000000000000003
---[ end trace f3e8fd1e1b2680bc ]---