bisecting fixing commit since 7d120bf21c05cbe30a679f0feeca884eeaceb069
building syzkaller on 79b211f74b08737aeb4934c6ff69a263b3c38013
testing commit 7d120bf21c05cbe30a679f0feeca884eeaceb069 with gcc (GCC) 8.1.0
kernel signature: c8034b8eb259afb5ba3025afd69eb4ec9afa62e49aa11b1065f16fbdfbb4df66
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
testing current HEAD 93556fb211fa7f1e18f869bdce0c225c25594942
testing commit 93556fb211fa7f1e18f869bdce0c225c25594942 with gcc (GCC) 8.1.0
kernel signature: a6f1e12ae583e81094e336e78b85a7c027acd35c311824dd1b5a003b9abca766
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
revisions tested: 2, total time: 25m46.933064494s (build: 18m9.814262596s, test: 6m50.802144452s)
the crash still happens on HEAD
commit msg: Linux 4.19.111
crash: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
8021q: adding VLAN 0 to HW filter on device batadv0
IPv6: ADDRCONF(NETDEV_UP): veth1_to_bridge: link is not ready
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not ready
BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
PGD a7cf3067 P4D a7cf3067 PUD 7c1c0067 PMD 0 
IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 7399 Comm: syz-executor.0 Not tainted 4.19.111-syzkaller #0
IPv6: ADDRCONF(NETDEV_UP): vxcan0: link is not ready
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:writew arch/x86/include/asm/io.h:66 [inline]
RIP: 0010:mem16_serial_out+0x61/0xa0 drivers/tty/serial/8250/8250_port.c:413
Code: b6 8b e1 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 24 48 63 f6 48 03 73 40 <66> 89 16 48 83 c4 08 5b 5d c3 89 55 f0 89 75 f4 e8 da cf 1f fe 8b
RSP: 0018:ffff888096e9f7c0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff8abce0d0 RCX: 1ffffffff1579c22
RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffffffff8abce110
RBP: ffff888096e9f7d0 R08: ffffed104326c1d6 R09: ffffed104326c1d5
R10: ffffed104326c1d5 R11: ffff888219360eab R12: ffffffff8abce120
R13: ffffffff8abce0d0 R14: ffffffff8abd39c0 R15: ffffffff8abce1ac
FS:  00007f38747f8700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 00000000a79fa000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 serial_out drivers/tty/serial/8250/8250.h:116 [inline]
 serial8250_clear_fifos.part.6+0x35/0xb0 drivers/tty/serial/8250/8250_port.c:556
 serial8250_clear_fifos drivers/tty/serial/8250/8250_port.c:555 [inline]
 serial8250_do_startup+0x34c/0x1b10 drivers/tty/serial/8250/8250_port.c:2194
 serial8250_startup+0x3f/0x50 drivers/tty/serial/8250/8250_port.c:2410
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
 uart_port_startup drivers/tty/serial/serial_core.c:218 [inline]
 uart_startup.part.19+0x38f/0x840 drivers/tty/serial/serial_core.c:257
 uart_startup drivers/tty/serial/serial_core.c:254 [inline]
 uart_set_info drivers/tty/serial/serial_core.c:997 [inline]
 uart_set_info_user drivers/tty/serial/serial_core.c:1025 [inline]
 uart_ioctl+0x12db/0x2bf0 drivers/tty/serial/serial_core.c:1348
 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669
8021q: adding VLAN 0 to HW filter on device batadv0
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688
8021q: adding VLAN 0 to HW filter on device batadv0
 ksys_ioctl+0x62/0x90 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a919
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f38747f7c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a919
RDX: 0000000020000240 RSI: 000000000000541f RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f38747f86d4
R13: 00000000004c5e04 R14: 00000000004dc270 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000002
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_bridge: link becomes ready
---[ end trace fb01c07cbe0427bc ]---
RIP: 0010:writew arch/x86/include/asm/io.h:66 [inline]
RIP: 0010:mem16_serial_out+0x61/0xa0 drivers/tty/serial/8250/8250_port.c:413
IPv6: ADDRCONF(NETDEV_CHANGE): bridge_slave_1: link becomes ready
Code: b6 8b e1 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 24 48 63 f6 48 03 73 40 <66> 89 16 48 83 c4 08 5b 5d c3 89 55 f0 89 75 f4 e8 da cf 1f fe 8b
bridge0: port 2(bridge_slave_1) entered blocking state
RSP: 0018:ffff888096e9f7c0 EFLAGS: 00010202
bridge0: port 2(bridge_slave_1) entered forwarding state
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
RAX: dffffc0000000000 RBX: ffffffff8abce0d0 RCX: 1ffffffff1579c22
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffffffff8abce110
IPv6: ADDRCONF(NETDEV_UP): veth0_to_bond: link is not ready
RBP: ffff888096e9f7d0 R08: ffffed104326c1d6 R09: ffffed104326c1d5
R10: ffffed104326c1d5 R11: ffff888219360eab R12: ffffffff8abce120
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_bond: link becomes ready
R13: ffffffff8abce0d0 R14: ffffffff8abd39c0 R15: ffffffff8abce1ac
FS:  00007f38747f8700(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000
IPv6: ADDRCONF(NETDEV_UP): veth1_to_bond: link is not ready
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_bond: link becomes ready
CR2: 0000000000000002 CR3: 00000000a79fa000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
IPv6: ADDRCONF(NETDEV_UP): veth0_to_team: link is not ready
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_team: link becomes ready