bisecting fixing commit since 1752938529c614a8ed4432ecce6ebc95d3b87207 building syzkaller on 5cc121d679e3f161f29503eeba9288431b6d644d testing commit 1752938529c614a8ed4432ecce6ebc95d3b87207 with gcc (GCC) 8.4.1 20210217 kernel signature: 8039b137857a0446099995660c8f0425df4ad7888dd6a84a42133fd4ba98cec6 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_change 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 run #10: crashed: possible deadlock in red_change run #11: crashed: possible deadlock in red_change run #12: crashed: possible deadlock in red_adaptative_timer run #13: crashed: possible deadlock in red_change run #14: crashed: possible deadlock in red_change run #15: crashed: possible deadlock in red_change run #16: crashed: possible deadlock in red_change run #17: crashed: possible deadlock in red_change run #18: crashed: possible deadlock in red_change run #19: crashed: possible deadlock in red_change testing current HEAD cb83ddcd5332fcc3efd52ba994976efc4dd6061e testing commit cb83ddcd5332fcc3efd52ba994976efc4dd6061e with gcc (GCC) 8.4.1 20210217 kernel signature: 1dbb94aa761492a9e81b54b4e97e7a4f4289cfe8fda56e73072c8b75e33b5845 all runs: crashed: possible deadlock in red_change revisions tested: 2, total time: 20m32.183303221s (build: 14m2.110463038s, test: 6m10.076379558s) the crash still happens on HEAD commit msg: Linux 4.14.226 crash: possible deadlock in red_change IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_0: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_batadv: link becomes ready ====================================================== WARNING: possible circular locking dependency detected 4.14.226-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.5/9656 is trying to acquire lock: (((&q->adapt_timer))){+.-.}, at: [] arch_local_irq_disable arch/x86/include/asm/paravirt.h:784 [inline] (((&q->adapt_timer))){+.-.}, at: [] arch_local_irq_save arch/x86/include/asm/paravirt.h:797 [inline] (((&q->adapt_timer))){+.-.}, at: [] del_timer_sync+0x76/0x1e0 kernel/time/timer.c:1235 but task is already holding lock: (&qdisc_rx_lock){+.-.}, at: [] spin_lock_bh include/linux/spinlock.h:322 [inline] (&qdisc_rx_lock){+.-.}, at: [] sch_tree_lock include/net/sch_generic.h:360 [inline] (&qdisc_rx_lock){+.-.}, at: [] red_change+0x3ee/0x1820 net/sched/sch_red.c:199 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&qdisc_rx_lock){+.-.}: lock_acquire+0x17e/0x3e0 kernel/locking/lockdep.c:3998 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:152 spin_lock include/linux/spinlock.h:317 [inline] red_adaptative_timer+0x72/0x550 net/sched/sch_red.c:233 call_timer_fn+0x142/0x570 kernel/time/timer.c:1280 expire_timers+0x299/0x440 kernel/time/timer.c:1319 __run_timers kernel/time/timer.c:1637 [inline] run_timer_softirq+0x1cd/0x540 kernel/time/timer.c:1650 __do_softirq+0x247/0x9a2 kernel/softirq.c:288 invoke_softirq kernel/softirq.c:368 [inline] irq_exit+0x15f/0x1a0 kernel/softirq.c:409 exiting_irq arch/x86/include/asm/apic.h:638 [inline] smp_apic_timer_interrupt+0x149/0x5d0 arch/x86/kernel/apic/apic.c:1106 apic_timer_interrupt+0x9a/0xa0 arch/x86/entry/entry_64.S:793 arch_local_irq_restore arch/x86/include/asm/paravirt.h:779 [inline] console_unlock+0xabf/0xe50 kernel/printk/printk.c:2408 vprintk_emit+0x32f/0x4e0 kernel/printk/printk.c:1923 vprintk_default+0x1a/0x20 kernel/printk/printk.c:1963 vprintk_func+0x49/0x130 kernel/printk/printk_safe.c:409 printk+0x91/0xab kernel/printk/printk.c:1996 batadv_check_known_mac_addr.cold.7+0x17/0x30 net/batman-adv/hard-interface.c:520 batadv_hard_if_event+0x1c7/0xda0 net/batman-adv/hard-interface.c:1030 notifier_call_chain+0xd6/0x150 kernel/notifier.c:93 __raw_notifier_call_chain kernel/notifier.c:394 [inline] raw_notifier_call_chain+0x11/0x20 kernel/notifier.c:401 call_netdevice_notifiers_info+0x4b/0x60 net/core/dev.c:1667 call_netdevice_notifiers net/core/dev.c:1683 [inline] dev_set_mac_address net/core/dev.c:6962 [inline] dev_set_mac_address+0x1b8/0x2f0 net/core/dev.c:6947 do_setlink+0x5d9/0x2c80 net/core/rtnetlink.c:2047 rtnl_newlink+0xeda/0x1610 net/core/rtnetlink.c:2660 rtnetlink_rcv_msg+0x34c/0x9e0 net/core/rtnetlink.c:4316 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 rtnetlink_rcv+0x10/0x20 net/core/rtnetlink.c:4328 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 SYSC_sendto net/socket.c:1763 [inline] SyS_sendto+0x1e4/0x2c0 net/socket.c:1731 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb -> #0 (((&q->adapt_timer))){+.-.}: check_prev_add kernel/locking/lockdep.c:1905 [inline] check_prevs_add kernel/locking/lockdep.c:2022 [inline] validate_chain kernel/locking/lockdep.c:2464 [inline] __lock_acquire+0x32ee/0x42d0 kernel/locking/lockdep.c:3491 lock_acquire+0x17e/0x3e0 kernel/locking/lockdep.c:3998 del_timer_sync+0xa2/0x1e0 kernel/time/timer.c:1236 red_destroy+0x14/0x50 net/sched/sch_red.c:154 qdisc_destroy+0x119/0x2e0 net/sched/sch_generic.c:726 red_change+0x5ff/0x1820 net/sched/sch_red.c:205 qdisc_change net/sched/sch_api.c:1145 [inline] tc_modify_qdisc+0xaff/0x13e0 net/sched/sch_api.c:1411 rtnetlink_rcv_msg+0x34c/0x9e0 net/core/rtnetlink.c:4316 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 rtnetlink_rcv+0x10/0x20 net/core/rtnetlink.c:4328 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 ___sys_sendmsg+0x625/0x920 net/socket.c:2062 __sys_sendmsg+0xc1/0x140 net/socket.c:2096 SYSC_sendmsg net/socket.c:2107 [inline] SyS_sendmsg+0xd/0x20 net/socket.c:2103 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb 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.5/9656: #0: (rtnl_mutex){+.+.}, at: [] rtnl_lock net/core/rtnetlink.c:72 [inline] #0: (rtnl_mutex){+.+.}, at: [] rtnetlink_rcv_msg+0x2c0/0x9e0 net/core/rtnetlink.c:4311 #1: (&qdisc_rx_lock){+.-.}, at: [] spin_lock_bh include/linux/spinlock.h:322 [inline] #1: (&qdisc_rx_lock){+.-.}, at: [] sch_tree_lock include/net/sch_generic.h:360 [inline] #1: (&qdisc_rx_lock){+.-.}, at: [] red_change+0x3ee/0x1820 net/sched/sch_red.c:199 stack backtrace: CPU: 0 PID: 9656 Comm: syz-executor.5 Not tainted 4.14.226-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x14b/0x1e7 lib/dump_stack.c:58 print_circular_bug.isra.17.cold.40+0x2e3/0x41e kernel/locking/lockdep.c:1258 check_prev_add kernel/locking/lockdep.c:1905 [inline] check_prevs_add kernel/locking/lockdep.c:2022 [inline] validate_chain kernel/locking/lockdep.c:2464 [inline] __lock_acquire+0x32ee/0x42d0 kernel/locking/lockdep.c:3491 lock_acquire+0x17e/0x3e0 kernel/locking/lockdep.c:3998 del_timer_sync+0xa2/0x1e0 kernel/time/timer.c:1236 red_destroy+0x14/0x50 net/sched/sch_red.c:154 qdisc_destroy+0x119/0x2e0 net/sched/sch_generic.c:726 red_change+0x5ff/0x1820 net/sched/sch_red.c:205 qdisc_change net/sched/sch_api.c:1145 [inline] tc_modify_qdisc+0xaff/0x13e0 net/sched/sch_api.c:1411 rtnetlink_rcv_msg+0x34c/0x9e0 net/core/rtnetlink.c:4316 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 rtnetlink_rcv+0x10/0x20 net/core/rtnetlink.c:4328 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 ___sys_sendmsg+0x625/0x920 net/socket.c:2062 __sys_sendmsg+0xc1/0x140 net/socket.c:2096 SYSC_sendmsg net/socket.c:2107 [inline] SyS_sendmsg+0xd/0x20 net/socket.c:2103 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb RIP: 0033:0x465b09 RSP: 002b:00007f4efb554188 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: 00007ffe47a23cdf R14: 00007f4efb554300 R15: 0000000000022000