bisecting fixing commit since eb575cd5d7f60241d016fdd13a9e86d962093c9b
building syzkaller on aba2b2fb3544d9e42991237c13d8cada421deda5
testing commit eb575cd5d7f60241d016fdd13a9e86d962093c9b
compiler: gcc version 8.4.1 20210217 (GCC)
kernel signature: 77e0775a795ac9837349b1ac2ad9bf88c8871cabbec78c3eb8f751537d7756de
run #0: crashed: WARNING in tcp_cwnd_reduction
run #1: crashed: divide error in tcp_reno_cong_avoid
run #2: crashed: divide error in tcp_reno_cong_avoid
run #3: crashed: divide error in tcp_reno_cong_avoid
run #4: crashed: divide error in tcp_reno_cong_avoid
run #5: crashed: divide error in tcp_reno_cong_avoid
run #6: crashed: divide error in tcp_reno_cong_avoid
run #7: crashed: WARNING in tcp_cwnd_reduction
run #8: crashed: divide error in tcp_reno_cong_avoid
run #9: crashed: divide error in tcp_reno_cong_avoid
run #10: OK
run #11: OK
run #12: OK
run #13: OK
run #14: OK
run #15: OK
run #16: OK
run #17: OK
run #18: OK
run #19: OK
testing current HEAD b172b44fcb1771e083aad806fa96f3f60e2ddfac
testing commit b172b44fcb1771e083aad806fa96f3f60e2ddfac
compiler: gcc version 8.4.1 20210217 (GCC)
kernel signature: 859784101b4bd59392ec0c660037dd25a01910346a58dfc1c510890166fc1fe6
run #0: crashed: divide error in tcp_reno_cong_avoid
run #1: crashed: divide error in tcp_reno_cong_avoid
run #2: crashed: divide error in tcp_reno_cong_avoid
run #3: crashed: divide error in tcp_reno_cong_avoid
run #4: crashed: WARNING in tcp_cwnd_reduction
run #5: crashed: WARNING in tcp_cwnd_reduction
run #6: crashed: divide error in tcp_reno_cong_avoid
run #7: crashed: WARNING in tcp_cwnd_reduction
run #8: OK
run #9: OK
revisions tested: 2, total time: 39m43.821668757s (build: 15m58.226881182s, test: 23m22.65200526s)
the crash still happens on HEAD
commit msg: Linux 4.19.206
crash: WARNING in tcp_cwnd_reduction
nf_conntrack: default automatic helper assignment has been turned off for security reasons and CT-based  firewall rule not found. Use the iptables CT target to attach helpers instead.
ieee802154 phy0 wpan0: encryption failed: -22
ieee802154 phy1 wpan1: encryption failed: -22
WARNING: CPU: 0 PID: 9 at net/ipv4/tcp_input.c:2472 tcp_cwnd_reduction+0x27f/0x3c0 net/ipv4/tcp_input.c:2482
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 4.19.206-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x17c/0x226 lib/dump_stack.c:118
 panic+0x1cd/0x375 kernel/panic.c:186
 __warn.cold.7+0x1b/0x36 kernel/panic.c:541
 report_bug+0x1a1/0x200 lib/bug.c:183
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 fixup_bug arch/x86/kernel/traps.c:173 [inline]
 do_error_trap+0x200/0x350 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:tcp_cwnd_reduction+0x27f/0x3c0 net/ipv4/tcp_input.c:2472
Code: 31 d2 4b 8d 44 30 ff 49 f7 f0 29 f8 eb 97 c3 41 29 fe 89 f0 41 39 f6 41 0f 4d c6 83 c0 01 44 39 e0 41 0f 4f c4 e9 7b ff ff ff <0f> 0b eb bf 89 55 d0 89 75 d4 e8 12 e4 12 fb 8b 55 d0 8b 75 d4 e9
RSP: 0018:ffff8880b59b7350 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8880af6f64c0 RCX: 0000000000000007
RDX: 0000000000005706 RSI: 0000000000000010 RDI: ffff8880af6f6d6c
RBP: ffff8880b59b7390 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 00000000fade3562 R12: 0000000000000010
R13: ffffffff8abb1a00 R14: ffff8880b59b7630 R15: 0000000000001204
 tcp_cong_control net/ipv4/tcp_input.c:3322 [inline]
 tcp_ack+0x2f1f/0x5740 net/ipv4/tcp_input.c:3715
 tcp_rcv_established+0x58d/0x1e60 net/ipv4/tcp_input.c:5666
 tcp_v4_do_rcv+0x52f/0x790 net/ipv4/tcp_ipv4.c:1547
 tcp_v4_rcv+0x2ab8/0x3bb0 net/ipv4/tcp_ipv4.c:1832
 ip_local_deliver_finish+0x3be/0x9a0 net/ipv4/ip_input.c:215
 NF_HOOK include/linux/netfilter.h:289 [inline]
 ip_local_deliver+0x164/0x4b0 net/ipv4/ip_input.c:256
 dst_input include/net/dst.h:461 [inline]
 ip_rcv_finish+0x159/0x240 net/ipv4/ip_input.c:414
 NF_HOOK include/linux/netfilter.h:289 [inline]
 ip_rcv+0xc1/0x2f0 net/ipv4/ip_input.c:524
 __netif_receive_skb_one_core+0x112/0x1a0 net/core/dev.c:4954
 __netif_receive_skb+0x1f/0x1b0 net/core/dev.c:5066
 process_backlog+0x220/0x710 net/core/dev.c:5849
 napi_poll net/core/dev.c:6280 [inline]
 net_rx_action+0x454/0xe30 net/core/dev.c:6346
 __do_softirq+0x25f/0x919 kernel/softirq.c:292
 run_ksoftirqd+0x5e/0x100 kernel/softirq.c:653
 smpboot_thread_fn+0x55f/0x8a0 kernel/smpboot.c:164
 kthread+0x347/0x410 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
Kernel Offset: disabled
Rebooting in 86400 seconds..