bisecting fixing commit since eb575cd5d7f60241d016fdd13a9e86d962093c9b building syzkaller on aba2b2fb3544d9e42991237c13d8cada421deda5 testing commit eb575cd5d7f60241d016fdd13a9e86d962093c9b with gcc (GCC) 8.4.1 20210217 kernel signature: 9e5de168318c2a6a4297345e2c0d2323b6641e3ce54f6e8e2bc0050519378125 run #0: crashed: divide error in tcp_reno_cong_avoid run #1: crashed: divide error in tcp_reno_cong_avoid run #2: crashed: WARNING in tcp_cwnd_reduction run #3: crashed: divide error in tcp_reno_cong_avoid run #4: crashed: divide error in tcp_reno_cong_avoid run #5: crashed: WARNING in tcp_cwnd_reduction run #6: crashed: WARNING in tcp_cwnd_reduction run #7: crashed: WARNING in tcp_cwnd_reduction run #8: crashed: WARNING in tcp_cwnd_reduction run #9: crashed: divide error in tcp_reno_cong_avoid run #10: crashed: divide error in tcp_reno_cong_avoid run #11: crashed: divide error in tcp_reno_cong_avoid run #12: crashed: WARNING in tcp_cwnd_reduction run #13: crashed: divide error in tcp_reno_cong_avoid run #14: OK run #15: OK run #16: OK run #17: OK run #18: OK run #19: OK testing current HEAD fcfbdfe9626edd5bf00c732e093eed249ecdbfa1 testing commit fcfbdfe9626edd5bf00c732e093eed249ecdbfa1 with gcc (GCC) 8.4.1 20210217 kernel signature: 9a59909c07baa7a5cecbcba5e690b0351a7f5378cf165614efe4555a2cb2d2bf 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: OK run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK reproducer seems to be flaky Reproducer flagged being flaky revisions tested: 2, total time: 44m32.821998417s (build: 20m42.378539621s, test: 23m23.776418053s) the crash still happens on HEAD commit msg: Linux 4.19.197 crash: divide error in tcp_reno_cong_avoid divide error: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 20058 Comm: syz-executor.2 Not tainted 4.19.197-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline] RIP: 0010:tcp_reno_cong_avoid+0x20c/0x2b0 net/ipv4/tcp_cong.c:456 Code: 45 39 f5 45 0f 47 ee 85 d2 45 89 ec 44 89 ab 98 08 00 00 0f 85 fa fe ff ff 48 83 c4 08 5b 41 5c 41 5d 41 5e 5d c3 89 d0 31 d2 <41> f7 f4 01 c1 89 93 9c 08 00 00 89 8b 98 08 00 00 e9 27 ff ff ff RSP: 0018:ffff8880ba3074b0 EFLAGS: 00010246 RAX: 0000000000000001 RBX: ffff8880a7842dc0 RCX: 0000000000000001 RDX: 0000000000000000 RSI: 000000008525c39b RDI: ffff8880a784365c RBP: ffff8880ba3074d8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 00000000ffffffff R15: 0000000000000001 FS: 00007f2ec2e8a700(0000) GS:ffff8880ba300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000004e4da5 CR3: 0000000097d7d000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: tcp_cdg_cong_avoid+0x121/0x1740 net/ipv4/tcp_cdg.c:292 tcp_cong_avoid net/ipv4/tcp_input.c:2972 [inline] tcp_cong_control net/ipv4/tcp_input.c:3325 [inline] tcp_ack+0x2a67/0x5740 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:5848 napi_poll net/core/dev.c:6272 [inline] net_rx_action+0x454/0xe30 net/core/dev.c:6338 __do_softirq+0x25f/0x919 kernel/softirq.c:292 do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1092 do_softirq kernel/softirq.c:336 [inline] do_softirq+0xfa/0x170 kernel/softirq.c:323 __local_bh_enable_ip+0x20b/0x250 kernel/softirq.c:189 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:176 [inline] _raw_spin_unlock_bh+0x30/0x40 kernel/locking/spinlock.c:200 spin_unlock_bh include/linux/spinlock.h:374 [inline] release_sock+0x11f/0x180 net/core/sock.c:2892 tcp_sendmsg+0x32/0x40 net/ipv4/tcp.c:1463 inet_sendmsg+0x108/0x440 net/ipv4/af_inet.c:798 sock_sendmsg_nosec net/socket.c:651 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:661 __sys_sendto+0x1f2/0x2e0 net/socket.c:1897 __do_sys_sendto net/socket.c:1909 [inline] __se_sys_sendto net/socket.c:1905 [inline] __x64_sys_sendto+0xdc/0x1a0 net/socket.c:1905 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x4665d9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f2ec2e8a188 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 000000000056c038 RCX: 00000000004665d9 RDX: 00000000fffffd46 RSI: 0000000020000240 RDI: 0000000000000004 RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 00000000000001f4 R10: 00000000000081f4 R11: 0000000000000246 R12: 000000000056c038 R13: 00007ffe7d182ccf R14: 00007f2ec2e8a300 R15: 0000000000022000 Modules linked in: ---[ end trace 8c1af547803a3d52 ]--- RIP: 0010:tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline] RIP: 0010:tcp_reno_cong_avoid+0x20c/0x2b0 net/ipv4/tcp_cong.c:456 Code: 45 39 f5 45 0f 47 ee 85 d2 45 89 ec 44 89 ab 98 08 00 00 0f 85 fa fe ff ff 48 83 c4 08 5b 41 5c 41 5d 41 5e 5d c3 89 d0 31 d2 <41> f7 f4 01 c1 89 93 9c 08 00 00 89 8b 98 08 00 00 e9 27 ff ff ff RSP: 0018:ffff8880ba3074b0 EFLAGS: 00010246 RAX: 0000000000000001 RBX: ffff8880a7842dc0 RCX: 0000000000000001 RDX: 0000000000000000 RSI: 000000008525c39b RDI: ffff8880a784365c RBP: ffff8880ba3074d8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 00000000ffffffff R15: 0000000000000001 FS: 00007f2ec2e8a700(0000) GS:ffff8880ba300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000004e4da5 CR3: 0000000097d7d000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400