bisecting fixing commit since 3207316b3beec7e38e5dbe2f463df0cec71e0b97 building syzkaller on 5cc121d679e3f161f29503eeba9288431b6d644d testing commit 3207316b3beec7e38e5dbe2f463df0cec71e0b97 with gcc (GCC) 8.4.1 20210217 kernel signature: 93c930dea59236755a1408604c4fe7548550d70b5feebd724137efd33b6208af run #0: crashed: possible deadlock in red_change run #1: crashed: possible deadlock in red_change run #2: crashed: possible deadlock in red_change run #3: crashed: possible deadlock in red_change run #4: crashed: possible deadlock in red_change run #5: crashed: possible deadlock in red_adaptative_timer run #6: crashed: possible deadlock in red_change run #7: crashed: possible deadlock in red_change run #8: crashed: possible deadlock in red_change run #9: crashed: possible deadlock in red_change testing current HEAD 255b58a2b3af0baa0ee11507390349217b8b73b0 testing commit 255b58a2b3af0baa0ee11507390349217b8b73b0 with gcc (GCC) 8.4.1 20210217 kernel signature: 3c448704156ebf841bcc6e74937ffcf087f67fa153b9ed717b41f5ca0239705a all runs: crashed: possible deadlock in red_change revisions tested: 2, total time: 21m49.927694608s (build: 14m56.727620036s, test: 6m0.374138543s) the crash still happens on HEAD commit msg: Linux 4.19.176 crash: possible deadlock in red_change IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 ====================================================== WARNING: possible circular locking dependency detected 4.19.176-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.0/10200 is trying to acquire lock: 00000000293e7f07 ((&q->adapt_timer)){+.-.}, at: arch_local_irq_disable arch/x86/include/asm/paravirt.h:794 [inline] 00000000293e7f07 ((&q->adapt_timer)){+.-.}, at: arch_local_irq_save arch/x86/include/asm/paravirt.h:807 [inline] 00000000293e7f07 ((&q->adapt_timer)){+.-.}, at: del_timer_sync+0x76/0x1e0 kernel/time/timer.c:1294 but task is already holding lock: 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: spin_lock_bh include/linux/spinlock.h:334 [inline] 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: sch_tree_lock include/net/sch_generic.h:477 [inline] 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: red_change+0x40a/0x1a60 net/sched/sch_red.c:230 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: IPVS: ftp: loaded support on port[0] = 21 -> #1 (&qdisc_rx_lock){+.-.}: __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144 spin_lock include/linux/spinlock.h:329 [inline] red_adaptative_timer+0x94/0x540 net/sched/sch_red.c:265 call_timer_fn+0x14c/0x510 kernel/time/timer.c:1338 expire_timers+0x255/0x3a0 kernel/time/timer.c:1375 __run_timers kernel/time/timer.c:1696 [inline] run_timer_softirq+0x1dc/0x570 kernel/time/timer.c:1709 __do_softirq+0x25f/0x919 kernel/softirq.c:292 invoke_softirq kernel/softirq.c:372 [inline] irq_exit+0x17f/0x1c0 kernel/softirq.c:412 exiting_irq arch/x86/include/asm/apic.h:535 [inline] smp_apic_timer_interrupt+0x13e/0x540 arch/x86/kernel/apic/apic.c:1098 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:894 arch_local_irq_restore arch/x86/include/asm/paravirt.h:789 [inline] lock_release+0x44b/0x840 kernel/locking/lockdep.c:3929 rcu_lock_release include/linux/rcupdate.h:247 [inline] rcu_read_unlock include/linux/rcupdate.h:681 [inline] inet_twsk_purge+0x484/0x680 net/ipv4/inet_timewait_sock.c:298 dccp_v6_exit_batch+0x15/0x20 net/dccp/ipv6.c:1113 ops_exit_list.isra.0+0xd3/0x120 net/core/net_namespace.c:156 setup_net+0x3a9/0x660 net/core/net_namespace.c:332 copy_net_ns+0x1b4/0x2a0 net/core/net_namespace.c:438 create_new_namespaces+0x483/0x750 kernel/nsproxy.c:107 copy_namespaces+0x22b/0x2b0 kernel/nsproxy.c:165 copy_process.part.2+0x3524/0x7960 kernel/fork.c:1915 copy_process kernel/fork.c:1718 [inline] _do_fork+0x166/0xc30 kernel/fork.c:2218 __do_sys_clone kernel/fork.c:2325 [inline] __se_sys_clone kernel/fork.c:2319 [inline] __x64_sys_clone+0xba/0x140 kernel/fork.c:2319 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 ((&q->adapt_timer)){+.-.}: lock_acquire+0x180/0x3a0 kernel/locking/lockdep.c:3907 del_timer_sync+0xa2/0x1e0 kernel/time/timer.c:1295 red_destroy+0x14/0x60 net/sched/sch_red.c:182 qdisc_destroy+0x128/0x650 net/sched/sch_generic.c:983 red_change+0x626/0x1a60 net/sched/sch_red.c:236 qdisc_change net/sched/sch_api.c:1240 [inline] tc_modify_qdisc+0xbd9/0x18e0 net/sched/sch_api.c:1543 rtnetlink_rcv_msg+0x34f/0x950 net/core/rtnetlink.c:4778 netlink_rcv_skb+0x13e/0x3d0 net/netlink/af_netlink.c:2455 rtnetlink_rcv+0x10/0x20 net/core/rtnetlink.c:4796 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x443/0x660 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x667/0xc60 net/netlink/af_netlink.c:1909 sock_sendmsg_nosec net/socket.c:622 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:632 ___sys_sendmsg+0x647/0x950 net/socket.c:2115 __sys_sendmsg+0xd9/0x180 net/socket.c:2153 __do_sys_sendmsg net/socket.c:2162 [inline] __se_sys_sendmsg net/socket.c:2160 [inline] __x64_sys_sendmsg+0x73/0xb0 net/socket.c:2160 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&qdisc_rx_lock); lock((&q->adapt_timer)); lock(&qdisc_rx_lock); lock((&q->adapt_timer)); *** DEADLOCK *** 2 locks held by syz-executor.0/10200: #0: 00000000f742d2a6 (rtnl_mutex){+.+.}, at: rtnl_lock net/core/rtnetlink.c:77 [inline] #0: 00000000f742d2a6 (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x301/0x950 net/core/rtnetlink.c:4775 #1: 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: spin_lock_bh include/linux/spinlock.h:334 [inline] #1: 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: sch_tree_lock include/net/sch_generic.h:477 [inline] #1: 000000001c51b27e (&qdisc_rx_lock){+.-.}, at: red_change+0x40a/0x1a60 net/sched/sch_red.c:230 stack backtrace: CPU: 0 PID: 10200 Comm: syz-executor.0 Not tainted 4.19.176-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 print_circular_bug.isra.17.cold.34+0x2e3/0x41e kernel/locking/lockdep.c:1221 check_prev_add kernel/locking/lockdep.c:1865 [inline] check_prevs_add kernel/locking/lockdep.c:1978 [inline] validate_chain kernel/locking/lockdep.c:2419 [inline] __lock_acquire+0x35c2/0x47c0 kernel/locking/lockdep.c:3415 lock_acquire+0x180/0x3a0 kernel/locking/lockdep.c:3907 del_timer_sync+0xa2/0x1e0 kernel/time/timer.c:1295 red_destroy+0x14/0x60 net/sched/sch_red.c:182 qdisc_destroy+0x128/0x650 net/sched/sch_generic.c:983 red_change+0x626/0x1a60 net/sched/sch_red.c:236 qdisc_change net/sched/sch_api.c:1240 [inline] tc_modify_qdisc+0xbd9/0x18e0 net/sched/sch_api.c:1543 rtnetlink_rcv_msg+0x34f/0x950 net/core/rtnetlink.c:4778 netlink_rcv_skb+0x13e/0x3d0 net/netlink/af_netlink.c:2455 rtnetlink_rcv+0x10/0x20 net/core/rtnetlink.c:4796 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x443/0x660 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x667/0xc60 net/netlink/af_netlink.c:1909 sock_sendmsg_nosec net/socket.c:622 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:632 ___sys_sendmsg+0x647/0x950 net/socket.c:2115 __sys_sendmsg+0xd9/0x180 net/socket.c:2153 __do_sys_sendmsg net/socket.c:2162 [inline] __se_sys_sendmsg net/socket.c:2160 [inline] __x64_sys_sendmsg+0x73/0xb0 net/socket.c:2160 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x465b09 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:00007fdb5befe188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000465b09 RDX: 0000000000000000 RSI: 00000000200007c0 RDI: 0000000000000006 RBP: 00000000004b069f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007fff2059117f R14: 00007fdb5befe300 R15: 0000000000022000 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21 IPVS: ftp: loaded support on port[0] = 21