bisecting fixing commit since a844dc4c544291470aa69edbe2434b040794e269
building syzkaller on 4b83c8fbed7b9cea831be880ec8aa1098b465f25
testing commit a844dc4c544291470aa69edbe2434b040794e269 with gcc (GCC) 8.1.0
kernel signature: ee847e14db64f053677cabf6624dd34bc75173a1d7a418c51099652f4b712b4c
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
testing current HEAD c6db52a88798e5a0dfef80041ad4d33cc8cf04eb
testing commit c6db52a88798e5a0dfef80041ad4d33cc8cf04eb with gcc (GCC) 8.1.0
kernel signature: 71966b39039f9d9f00a00602e2897b9ee67f2c070383a3aca2111edb4ebc70b6
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
revisions tested: 2, total time: 23m10.746921276s (build: 16m33.305174387s, test: 6m2.445891129s)
the crash still happens on HEAD
commit msg: Linux 4.14.183
crash: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out
bridge0: port 2(bridge_slave_1) entered blocking state
bridge0: port 2(bridge_slave_1) entered forwarding state
IPv6: ADDRCONF(NETDEV_UP): bridge0: link is not ready
IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
BUG: unable to handle kernel NULL pointer dereference at 0000000000000003
IPv6: ADDRCONF(NETDEV_UP): veth0_to_bond: link is not 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 83168067 P4D 83168067 PUD 8f3cb067 PMD 0 
IPv6: ADDRCONF(NETDEV_UP): veth1_to_bond: link is not ready
Oops: 0002 [#1] PREEMPT SMP KASAN
IPv6: ADDRCONF(NETDEV_UP): veth0_to_team: link is not ready
Modules linked in:
IPv6: ADDRCONF(NETDEV_UP): veth1_to_team: link is not ready
CPU: 0 PID: 7301 Comm: syz-executor.1 Not tainted 4.14.183-syzkaller #0
IPv6: ADDRCONF(NETDEV_UP): veth0_to_hsr: link is not ready
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff88808dbe4680 task.stack: ffff88808e788000
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:ffff88808e78f8c0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff8a460dd0 RCX: 1ffffffff148c1c2
RDX: 00000000000000bf RSI: 0000000000000003 RDI: ffffffff8a460e10
RBP: ffff88808e78f8d0 R08: ffff88808dbe4f50 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8a460f10
R13: ffffffff8a460dd0 R14: ffffffff8a460e20 R15: ffffffff8a460e9c
IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready
FS:  00007f943e79a700(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000003 CR3: 000000008f3d7000 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
hsr0: Slave A (hsr_slave_0) is not up; please bring it up to get a fully working HSR network
 uart_port_startup drivers/tty/serial/serial_core.c:231 [inline]
 uart_startup.part.19+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+0x126b/0x2b80 drivers/tty/serial/serial_core.c:1361
hsr0: Slave B (hsr_slave_1) is not up; please bring it up to get a fully working HSR network
 tty_ioctl+0x434/0x1260 drivers/tty/tty_io.c:2661
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not 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): vxcan0: link is not ready
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
8021q: adding VLAN 0 to HW filter on device batadv0
 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+0x46/0xbb
RIP: 0033:0x45a6f9
RSP: 002b:00007f943e799c78 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: 00007f943e79a6d4
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 fb 3b 37 fe 8b 
RIP: writeb arch/x86/include/asm/io.h:65 [inline] RSP: ffff88808e78f8c0
RIP: mem_serial_out+0x61/0x90 drivers/tty/serial/8250/8250_port.c:408 RSP: ffff88808e78f8c0
CR2: 0000000000000003
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_bond: link becomes ready
---[ end trace 6c5a1e98365128cc ]---
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_bond: link becomes ready