On Mon, May 14, 2018 at 9:34 PM, Neil Horman <nhor...@tuxdriver.com> wrote: > On Fri, May 11, 2018 at 12:00:38PM +0200, Dmitry Vyukov wrote: >> On Mon, Apr 30, 2018 at 8:09 PM, syzbot >> <syzbot+fc78715ba3b3257ca...@syzkaller.appspotmail.com> wrote: >> > Hello, >> > >> > syzbot found the following crash on: >> > >> > HEAD commit: 5d1365940a68 Merge >> > git://git.kernel.org/pub/scm/linux/kerne... >> > git tree: net-next >> > console output: https://syzkaller.appspot.com/x/log.txt?id=5667997129637888 >> > kernel config: >> > https://syzkaller.appspot.com/x/.config?id=-5947642240294114534 >> > dashboard link: >> > https://syzkaller.appspot.com/bug?extid=fc78715ba3b3257caf6a >> > compiler: gcc (GCC) 8.0.1 20180413 (experimental) >> > >> > Unfortunately, I don't have any reproducer for this crash yet. >> >> This looks sctp-related, +sctp maintainers. >> > Looking at the entire trace, it appears that we are getting caught in the > kfree_skb that is getting triggered in enqueue_to_backlog which occurs when > our > rx backlog list grows over netdev_max_backlog packets. That suggests to me > that It might be a long skb->frag_list that made kfree_skb slow when packing lots of small chunks to go through lo device?
> whatever test(s) is/are causing this trace are queuing up a large number of > frames to be sent over the loopback interface, and are never/rarely getting > received. Looking up higher in the stack, in the > sctp_generate_heartbeat_event > function, we (in addition to the rcu_read_lock in sctp_v6_xmit) we also hold > the > socket lock during the entirety of the xmit operaion. Is it possible that we > are just enqueuing so many frames for xmit that we are blocking progress of > other threads using the same socket that we cross the RCU self detected stall > boundary? While its not a fix per se, it might be a worthwhile test to limit > the number of frames we flush in a single pass. > > Neil > >> > IMPORTANT: if you fix the bug, please add the following tag to the commit: >> > Reported-by: syzbot+fc78715ba3b3257ca...@syzkaller.appspotmail.com >> > >> > INFO: rcu_sched self-detected stall on CPU >> > 1-...!: (1 GPs behind) idle=a3e/1/4611686018427387908 >> > softirq=71980/71983 fqs=33 >> > (t=125000 jiffies g=39438 c=39437 q=958) >> > rcu_sched kthread starved for 124829 jiffies! g39438 c39437 f0x0 >> > RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0 >> > RCU grace-period kthread stack dump: >> > rcu_sched R running task 23768 9 2 0x80000000 >> > Call Trace: >> > context_switch kernel/sched/core.c:2848 [inline] >> > __schedule+0x801/0x1e30 kernel/sched/core.c:3490 >> > schedule+0xef/0x430 kernel/sched/core.c:3549 >> > schedule_timeout+0x138/0x240 kernel/time/timer.c:1801 >> > rcu_gp_kthread+0x6b5/0x1940 kernel/rcu/tree.c:2231 >> > kthread+0x345/0x410 kernel/kthread.c:238 >> > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411 >> > NMI backtrace for cpu 1 >> > CPU: 1 PID: 20560 Comm: syz-executor4 Not tainted 4.16.0+ #1 >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >> > Google 01/01/2011 >> > Call Trace: >> > <IRQ> >> > __dump_stack lib/dump_stack.c:77 [inline] >> > dump_stack+0x1b9/0x294 lib/dump_stack.c:113 >> > nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103 >> > nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62 >> > arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 >> > trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline] >> > rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1376 >> > print_cpu_stall kernel/rcu/tree.c:1525 [inline] >> > check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593 >> > __rcu_pending kernel/rcu/tree.c:3356 [inline] >> > rcu_pending kernel/rcu/tree.c:3401 [inline] >> > rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763 >> > update_process_times+0x2d/0x70 kernel/time/timer.c:1636 >> > tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:173 >> > tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1283 >> > __run_hrtimer kernel/time/hrtimer.c:1386 [inline] >> > __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1448 >> > hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1506 >> > local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline] >> > smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050 >> > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862 >> > RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783 >> > [inline] >> > RIP: 0010:kmem_cache_free+0xb3/0x2d0 mm/slab.c:3757 >> > RSP: 0018:ffff8801db105228 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13 >> > RAX: 0000000000000007 RBX: ffff8800b055c940 RCX: 1ffff1003b2345a5 >> > RDX: 0000000000000000 RSI: ffff8801d91a2d80 RDI: 0000000000000282 >> > RBP: ffff8801db105248 R08: ffff8801d91a2cb8 R09: 0000000000000002 >> > R10: ffff8801d91a2480 R11: 0000000000000000 R12: ffff8801d9848e40 >> > R13: 0000000000000282 R14: ffffffff85b7f27c R15: 0000000000000000 >> > kfree_skbmem+0x13c/0x210 net/core/skbuff.c:582 >> > __kfree_skb net/core/skbuff.c:642 [inline] >> > kfree_skb+0x19d/0x560 net/core/skbuff.c:659 >> > enqueue_to_backlog+0x2fc/0xc90 net/core/dev.c:3968 >> > netif_rx_internal+0x14d/0xae0 net/core/dev.c:4181 >> > netif_rx+0xba/0x400 net/core/dev.c:4206 >> > loopback_xmit+0x283/0x741 drivers/net/loopback.c:91 >> > __netdev_start_xmit include/linux/netdevice.h:4087 [inline] >> > netdev_start_xmit include/linux/netdevice.h:4096 [inline] >> > xmit_one net/core/dev.c:3053 [inline] >> > dev_hard_start_xmit+0x264/0xc10 net/core/dev.c:3069 >> > __dev_queue_xmit+0x2724/0x34c0 net/core/dev.c:3584 >> > dev_queue_xmit+0x17/0x20 net/core/dev.c:3617 >> > neigh_hh_output include/net/neighbour.h:472 [inline] >> > neigh_output include/net/neighbour.h:480 [inline] >> > ip6_finish_output2+0x134e/0x2810 net/ipv6/ip6_output.c:120 >> > ip6_finish_output+0x5fe/0xbc0 net/ipv6/ip6_output.c:154 >> > NF_HOOK_COND include/linux/netfilter.h:277 [inline] >> > ip6_output+0x227/0x9b0 net/ipv6/ip6_output.c:171 >> > dst_output include/net/dst.h:444 [inline] >> > NF_HOOK include/linux/netfilter.h:288 [inline] >> > ip6_xmit+0xf51/0x23f0 net/ipv6/ip6_output.c:277 >> > sctp_v6_xmit+0x4a5/0x6b0 net/sctp/ipv6.c:225 >> > sctp_packet_transmit+0x26f6/0x3ba0 net/sctp/output.c:650 >> > sctp_outq_flush+0x1373/0x4370 net/sctp/outqueue.c:1197 >> > sctp_outq_uncork+0x6a/0x80 net/sctp/outqueue.c:776 >> > sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1820 [inline] >> > sctp_side_effects net/sctp/sm_sideeffect.c:1220 [inline] >> > sctp_do_sm+0x596/0x7160 net/sctp/sm_sideeffect.c:1191 >> > sctp_generate_heartbeat_event+0x218/0x450 net/sctp/sm_sideeffect.c:406 >> > call_timer_fn+0x230/0x940 kernel/time/timer.c:1326 >> > expire_timers kernel/time/timer.c:1363 [inline] >> > __run_timers+0x79e/0xc50 kernel/time/timer.c:1666 >> > run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692 >> > __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285 >> > invoke_softirq kernel/softirq.c:365 [inline] >> > irq_exit+0x1d1/0x200 kernel/softirq.c:405 >> > exiting_irq arch/x86/include/asm/apic.h:525 [inline] >> > smp_apic_timer_interrupt+0x17e/0x710 arch/x86/kernel/apic/apic.c:1052 >> > apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862 >> > </IRQ> >> > RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783 >> > [inline] >> > RIP: 0010:lock_release+0x4d4/0xa10 kernel/locking/lockdep.c:3942 >> > RSP: 0018:ffff8801971ce7b0 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13 >> > RAX: dffffc0000000000 RBX: 1ffff10032e39cfb RCX: 1ffff1003b234595 >> > RDX: 1ffffffff11630ed RSI: 0000000000000002 RDI: 0000000000000282 >> > RBP: ffff8801971ce8e0 R08: 1ffff10032e39cff R09: ffffed003b6246c2 >> > R10: 0000000000000003 R11: 0000000000000001 R12: ffff8801d91a2480 >> > R13: ffffffff88b8df60 R14: ffff8801d91a2480 R15: ffff8801971ce7f8 >> > rcu_lock_release include/linux/rcupdate.h:251 [inline] >> > rcu_read_unlock include/linux/rcupdate.h:688 [inline] >> > __unlock_page_memcg+0x72/0x100 mm/memcontrol.c:1654 >> > unlock_page_memcg+0x2c/0x40 mm/memcontrol.c:1663 >> > page_remove_file_rmap mm/rmap.c:1248 [inline] >> > page_remove_rmap+0x6f2/0x1250 mm/rmap.c:1299 >> > zap_pte_range mm/memory.c:1337 [inline] >> > zap_pmd_range mm/memory.c:1441 [inline] >> > zap_pud_range mm/memory.c:1470 [inline] >> > zap_p4d_range mm/memory.c:1491 [inline] >> > unmap_page_range+0xeb4/0x2200 mm/memory.c:1512 >> > unmap_single_vma+0x1a0/0x310 mm/memory.c:1557 >> > unmap_vmas+0x120/0x1f0 mm/memory.c:1587 >> > exit_mmap+0x265/0x570 mm/mmap.c:3038 >> > __mmput kernel/fork.c:962 [inline] >> > mmput+0x251/0x610 kernel/fork.c:983 >> > exit_mm kernel/exit.c:544 [inline] >> > do_exit+0xe98/0x2730 kernel/exit.c:852 >> > do_group_exit+0x16f/0x430 kernel/exit.c:968 >> > get_signal+0x886/0x1960 kernel/signal.c:2469 >> > do_signal+0x98/0x2040 arch/x86/kernel/signal.c:810 >> > exit_to_usermode_loop+0x28a/0x310 arch/x86/entry/common.c:162 >> > prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline] >> > syscall_return_slowpath arch/x86/entry/common.c:265 [inline] >> > do_syscall_64+0x792/0x9d0 arch/x86/entry/common.c:292 >> > entry_SYSCALL_64_after_hwframe+0x42/0xb7 >> > RIP: 0033:0x455319 >> > RSP: 002b:00007fa346e81ce8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca >> > RAX: fffffffffffffe00 RBX: 000000000072bf80 RCX: 0000000000455319 >> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000072bf80 >> > RBP: 000000000072bf80 R08: 0000000000000000 R09: 000000000072bf58 >> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 >> > R13: 0000000000a3e81f R14: 00007fa346e829c0 R15: 0000000000000001 >> > >> > >> > --- >> > This bug is generated by a bot. It may contain errors. >> > See https://goo.gl/tpsmEJ for more information about syzbot. >> > syzbot engineers can be reached at syzkal...@googlegroups.com. >> > >> > syzbot will keep track of this bug report. >> > If you forgot to add the Reported-by tag, once the fix for this bug is >> > merged >> > into any tree, please reply to this email with: >> > #syz fix: exact-commit-title >> > To mark this as a duplicate of another syzbot report, please reply with: >> > #syz dup: exact-subject-of-another-report >> > If it's a one-off invalid bug report, please reply with: >> > #syz invalid >> > Note: if the crash happens again, it will cause creation of a new bug >> > report. >> > Note: all commands must start from beginning of the line in the email body. >> > >> > -- >> > You received this message because you are subscribed to the Google Groups >> > "syzkaller-bugs" group. >> > To unsubscribe from this group and stop receiving emails from it, send an >> > email to syzkaller-bugs+unsubscr...@googlegroups.com. >> > To view this discussion on the web visit >> > https://groups.google.com/d/msgid/syzkaller-bugs/000000000000a9b0e3056b14bfb2%40google.com. >> > For more options, visit https://groups.google.com/d/optout. >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in >> the body of a message to majord...@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
