Re: soft lockup - may be related to wireguard (backported)

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On 5/4/20 4:47 AM, Serge Belyshev wrote:
> Hi! I can reproduce similar RCU stall with a different kernel under
> specific conditions on a specific box:
> 
> [   54.437636] rcu: INFO: rcu_sched self-detected stall on CPU
> [   54.438838] rcu:  0-...!: (2101 ticks this GP) idle=ea6/1/0x4000000000000002 softirq=604/604 fqs=0
> [   54.440052]  (t=2101 jiffies g=69 q=89)
> [   54.441273] rcu: rcu_sched kthread starved for 2101 jiffies! g69 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
> [   54.442547] rcu: RCU grace-period kthread stack dump:
> [   54.443812] rcu_sched       I    0    10      2 0x80004000
> [   54.443814] Call Trace:
> [   54.445087]  ? __schedule+0x540/0xa80
> [   54.446356]  schedule+0x45/0xb0
> [   54.447612]  schedule_timeout+0x144/0x280
> [   54.448859]  ? __next_timer_interrupt+0xc0/0xc0
> [   54.450099]  rcu_gp_kthread+0x3f0/0x840
> [   54.451329]  kthread+0xe6/0x120
> [   54.452557]  ? rcu_gp_slow.part.0+0x30/0x30
> [   54.453761]  ? __kthread_create_on_node+0x150/0x150
> [   54.454943]  ret_from_fork+0x1f/0x30
> [   54.456095] NMI backtrace for cpu 0
> [   54.457221] CPU: 0 PID: 2910 Comm: md5sum Not tainted 5.6.0-00001-g6e142c237f00 #1309
> [   54.458355] Hardware name: Gigabyte Technology Co., Ltd. GA-MA790FX-DQ6/GA-MA790FX-DQ6, BIOS F7g 07/19/2010
> [   54.459484] Call Trace:
> [   54.460576]  <IRQ>
> [   54.461672]  dump_stack+0x50/0x70
> [   54.462772]  nmi_cpu_backtrace.cold+0x14/0x53
> [   54.463871]  ? lapic_can_unplug_cpu.cold+0x3e/0x3e
> [   54.464955]  nmi_trigger_cpumask_backtrace+0x7c/0x89
> [   54.466026]  rcu_dump_cpu_stacks+0x7b/0xa9
> [   54.467088]  rcu_sched_clock_irq.cold+0x153/0x38a
> [   54.468146]  update_process_times+0x1f/0x50
> [   54.469204]  tick_sched_timer+0x33/0x70
> [   54.470262]  ? tick_sched_do_timer+0x50/0x50
> [   54.471321]  __hrtimer_run_queues+0xe2/0x180
> [   54.472378]  hrtimer_interrupt+0x109/0x240
> [   54.473423]  smp_apic_timer_interrupt+0x48/0x80
> [   54.474461]  apic_timer_interrupt+0xf/0x20
> [   54.475486]  </IRQ>
> [   54.476495] RIP: 0033:0x556cbd33bf19
> [   54.477506] Code: ce 44 8b 4b 10 c1 c9 0f 01 d1 44 89 4c 24 c8 21 ce 31 c6 01 fe 41 8d bc 01 af 0f 7c f5 89 d0 44 8b 4b 3c c1 ce 0a 31 c8 01 ce <21> f0 31 d0 01 f8 41 8d bc 12 2a c6 87 47 89 ca 41 89 ea c1 c0 07
> [   54.479694] RSP: 002b:00007ffc30913ce8 EFLAGS: 00000283 ORIG_RAX: ffffffffffffff13
> [   54.480813] RAX: 00000000980270bd RBX: 0000556cbe81e4e0 RCX: 00000000c35c3b1a
> [   54.481943] RDX: 000000005b5e4ba7 RSI: 00000000ae8ee5ae RDI: 0000000009b5de85
> [   54.483075] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> [   54.484201] R10: 0000000000000000 R11: 00000000b16eb4f8 R12: 0000000000000000
> [   54.485317] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000023604445
> 

I don't see anything wireguard-related in this stacktrace. Can you try 
sending one that has something wireguard-related in it? Or is more complete?