bisecting fixing commit since 7d120bf21c05cbe30a679f0feeca884eeaceb069
building syzkaller on 79b211f74b08737aeb4934c6ff69a263b3c38013
testing commit 7d120bf21c05cbe30a679f0feeca884eeaceb069 with gcc (GCC) 8.1.0
kernel signature: 0493f3f6e3ffd3fe44c8af47b45f62fed375c855af619aca728c9f2fafee9f36
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
testing current HEAD 17a87580a8856170d59aab302226811a4ae69149
testing commit 17a87580a8856170d59aab302226811a4ae69149 with gcc (GCC) 8.1.0
kernel signature: ee7b3d1c1a22cdd69a6f095079828b6f0d4327359b2676a2e192bede8010e375
all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
revisions tested: 2, total time: 26m38.989378642s (build: 18m25.151439998s, test: 7m23.478202567s)
the crash still happens on HEAD
commit msg: Linux 4.19.133
crash: BUG: unable to handle kernel NULL pointer dereference in mem16_serial_out
IPv6: ADDRCONF(NETDEV_UP): veth1_to_team: link is not ready
IPv6: ADDRCONF(NETDEV_UP): veth0_to_hsr: link is not ready
8021q: adding VLAN 0 to HW filter on device batadv0
IPv6: ADDRCONF(NETDEV_UP): vxcan0: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_team: link becomes ready
BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
IPv6: ADDRCONF(NETDEV_CHANGE): team_slave_1: link becomes ready
PGD 8ced6067 P4D 8ced6067 PUD 8ced7067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7436 Comm: syz-executor.2 Not tainted 4.19.133-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_hsr: link becomes ready
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 0a 0f 1d fe 8b
RSP: 0018:ffff88809523f7c0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff8abd8190 RCX: 1ffffffff157b03a
RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffffffff8abd81d0
RBP: ffff88809523f7d0 R08: ffffed10432761d6 R09: ffffed10432761d5
R10: ffffed10432761d5 R11: ffff8882193b0eab R12: ffffffff8abd81e0
R13: ffffffff8abd8190 R14: ffffffff8abdda80 R15: ffffffff8abd826c
FS:  00007fc6957fa700(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 000000008b3e9000 CR4: 00000000001406e0
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
 uart_port_startup drivers/tty/serial/serial_core.c:218 [inline]
 uart_startup.part.18+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+0x12c8/0x2be0 drivers/tty/serial/serial_core.c:1348
 tty_ioctl+0x452/0x1290 drivers/tty/tty_io.c:2669
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688
 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
IPv6: ADDRCONF(NETDEV_CHANGE): hsr_slave_0: link becomes ready
RIP: 0033:0x45a999
Code: 2d 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 fb b5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc6957f9c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a999
RDX: 0000000020000240 RSI: 000000000000541f RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc6957fa6d4
R13: 00000000004c5e84 R14: 00000000004dc2f0 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000002
IPv6: ADDRCONF(NETDEV_UP): vxcan0: link is not ready
---[ end trace 2b4f7386312d54c6 ]---
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 0a 0f 1d fe 8b
IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_hsr: link becomes ready
RSP: 0018:ffff88809523f7c0 EFLAGS: 00010202
IPv6: ADDRCONF(NETDEV_CHANGE): hsr_slave_1: link becomes ready
RAX: dffffc0000000000 RBX: ffffffff8abd8190 RCX: 1ffffffff157b03a
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffffffff8abd81d0
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
RBP: ffff88809523f7d0 R08: ffffed10432761d6 R09: ffffed10432761d5
IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
R10: ffffed10432761d5 R11: ffff8882193b0eab R12: ffffffff8abd81e0
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not ready
R13: ffffffff8abd8190 R14: ffffffff8abdda80 R15: ffffffff8abd826c
IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
FS:  00007fc6957fa700(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f138154a740 CR3: 000000008b3e9000 CR4: 00000000001406e0
8021q: adding VLAN 0 to HW filter on device batadv0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400