Hello,
syzbot found the following crash on:
HEAD commit: 3b47fd5c Merge tag 'nfs-for-5.3-4' of git://git.linux-nfs...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12983001600000
kernel config: https://syzkaller.appspot.com/x/.config?x=b89bb446a3faaba4
dashboard link: https://syzkaller.appspot.com/bug?extid=2addc1f058bd021b0a40
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17d8afae600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1253d1fa600000
Bisection is inconclusive: the bug happens on the oldest tested release.
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=109dcfc6600000
console output: https://syzkaller.appspot.com/x/log.txt?x=149dcfc6600000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2addc1f058bd021b0...@syzkaller.appspotmail.com
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-...!: (10500 ticks this GP) idle=c4e/1/0x4000000000000002
softirq=10445/10445 fqs=0
(t=10500 jiffies g=10669 q=248)
rcu: rcu_preempt kthread starved for 10500 jiffies! g10669 f0x0
RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt I29392 10 2 0x80004000
Call Trace:
context_switch kernel/sched/core.c:3254 [inline]
__schedule+0x755/0x1580 kernel/sched/core.c:3880
schedule+0xd9/0x260 kernel/sched/core.c:3947
schedule_timeout+0x486/0xc50 kernel/time/timer.c:1807
rcu_gp_fqs_loop kernel/rcu/tree.c:1611 [inline]
rcu_gp_kthread+0x9b2/0x18c0 kernel/rcu/tree.c:1768
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 0
CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.3.0-rc7+ #0
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+0x172/0x1f0 lib/dump_stack.c:113
nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x23b/0x28b 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:164 [inline]
rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree_stall.h:254
print_cpu_stall kernel/rcu/tree_stall.h:455 [inline]
check_cpu_stall kernel/rcu/tree_stall.h:529 [inline]
rcu_pending kernel/rcu/tree.c:2736 [inline]
rcu_sched_clock_irq.cold+0x4dd/0xc13 kernel/rcu/tree.c:2183
update_process_times+0x32/0x80 kernel/time/timer.c:1639
tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1296
__run_hrtimer kernel/time/hrtimer.c:1389 [inline]
__hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1451
hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1509
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1106 [inline]
smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1131
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
</IRQ>
RIP: 0010:write_comp_data+0x68/0x70 kernel/kcov.c:147
Code: 00 00 4e 8d 14 dd 28 00 00 00 4d 39 d0 72 1b 49 83 c1 01 4a 89 7c 10
e0 4a 89 74 10 e8 4a 89 54 10 f0 4a 89 4c d8 20 4c 89 08 <c3> 0f 1f 80 00
00 00 00 55 40 0f b6 d6 40 0f b6 f7 31 ff 48 89 e5
RSP: 0018:ffff8880a98be990 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000301 RBX: ffff88808c6eb0b8 RCX: ffffffff85c64b39
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: ffff8880a98be998 R08: ffff8880a98b2240 R09: 0000000000000000
R10: fffffbfff134af8f R11: ffff8880a98b2240 R12: dffffc0000000000
R13: ffff88808c6eadc0 R14: ffff88808c6eb150 R15: 0000000000000000
hhf_dequeue+0xb9/0xa20 net/sched/sch_hhf.c:434
dequeue_skb net/sched/sch_generic.c:258 [inline]
qdisc_restart net/sched/sch_generic.c:361 [inline]
__qdisc_run+0x1e7/0x19d0 net/sched/sch_generic.c:379
__dev_xmit_skb net/core/dev.c:3533 [inline]
__dev_queue_xmit+0x16f1/0x3650 net/core/dev.c:3838
dev_queue_xmit+0x18/0x20 net/core/dev.c:3902
br_dev_queue_push_xmit+0x3f3/0x5c0 net/bridge/br_forward.c:52
br_nf_dev_queue_xmit+0x34e/0x1470 net/bridge/br_netfilter_hooks.c:796
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
br_nf_post_routing+0x1502/0x1d30 net/bridge/br_netfilter_hooks.c:844
nf_hook_entry_hookfn include/linux/netfilter.h:135 [inline]
nf_hook_slow+0xbc/0x1e0 net/netfilter/core.c:512
nf_hook include/linux/netfilter.h:260 [inline]
NF_HOOK include/linux/netfilter.h:303 [inline]
br_forward_finish+0x215/0x400 net/bridge/br_forward.c:65
br_nf_hook_thresh+0x2e9/0x370 net/bridge/br_netfilter_hooks.c:1015
br_nf_forward_finish+0x66c/0xa90 net/bridge/br_netfilter_hooks.c:560
NF_HOOK include/linux/netfilter.h:305 [inline]
NF_HOOK include/linux/netfilter.h:299 [inline]
br_nf_forward_ip net/bridge/br_netfilter_hooks.c:630 [inline]
br_nf_forward_ip+0xc74/0x21e0 net/bridge/br_netfilter_hooks.c:571
nf_hook_entry_hookfn include/linux/netfilter.h:135 [inline]
nf_hook_slow+0xbc/0x1e0 net/netfilter/core.c:512
nf_hook include/linux/netfilter.h:260 [inline]
NF_HOOK include/linux/netfilter.h:303 [inline]
__br_forward+0x393/0xb00 net/bridge/br_forward.c:109
deliver_clone+0x61/0xc0 net/bridge/br_forward.c:125
br_flood+0x325/0x3d0 net/bridge/br_forward.c:232
br_handle_frame_finish+0xb46/0x1670 net/bridge/br_input.c:162
br_nf_hook_thresh+0x2e9/0x370 net/bridge/br_netfilter_hooks.c:1015
br_nf_pre_routing_finish_ipv6+0x6fb/0xd80
net/bridge/br_netfilter_ipv6.c:206
NF_HOOK include/linux/netfilter.h:305 [inline]
br_nf_pre_routing_ipv6+0x456/0x832 net/bridge/br_netfilter_ipv6.c:236
br_nf_pre_routing+0x1743/0x2355 net/bridge/br_netfilter_hooks.c:501
nf_hook_entry_hookfn include/linux/netfilter.h:135 [inline]
nf_hook_bridge_pre net/bridge/br_input.c:223 [inline]
br_handle_frame+0x806/0x133e net/bridge/br_input.c:348
__netif_receive_skb_core+0xfc1/0x3060 net/core/dev.c:4905
__netif_receive_skb_one_core+0xa8/0x1a0 net/core/dev.c:5002
__netif_receive_skb+0x2c/0x1d0 net/core/dev.c:5118
process_backlog+0x206/0x750 net/core/dev.c:5929
napi_poll net/core/dev.c:6352 [inline]
net_rx_action+0x4d6/0x1030 net/core/dev.c:6418
__do_softirq+0x262/0x98c kernel/softirq.c:292
run_ksoftirqd kernel/softirq.c:603 [inline]
run_ksoftirqd+0x8e/0x110 kernel/softirq.c:595
smpboot_thread_fn+0x6a3/0xa40 kernel/smpboot.c:165
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
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