circular locking dependency splat

[David Ahern <dsahern@gmail.com>]

Saw this trying to reproduce the RA splat. This is from top of tree
net-next:
commit 2798b80b385384d51a81832556ee9ad25d175f9b

[   99.988789] ======================================================
[   99.990494] WARNING: possible circular locking dependency detected
[   99.992187] 4.14.0-rc7+ #23 Not tainted
[   99.993242] ------------------------------------------------------
[   99.994937] swapper/1/0 is trying to acquire lock:
[   99.996272]  (slock-AF_INET){+.-.}, at: [<ffffffff81729b14>]
tcp_delack_timer+0x29/0xb1
[   99.998375]
but task is already holding lock:
[   99.999149]  ((timer)){+.-.}, at: [<ffffffff810f3c0b>]
call_timer_fn+0x5/0x36b
[  100.000105]
which lock already depends on the new lock.

[  100.001184]
the existing dependency chain (in reverse order) is:
[  100.002163]
-> #1 ((timer)){+.-.}:
[  100.002830]        lock_acquire+0x154/0x220
[  100.003392]        del_timer_sync+0x47/0xbd
[  100.003952]        inet_csk_reqsk_queue_drop+0x109/0x141
[  100.004654]        inet_csk_complete_hashdance+0x3b/0x68
[  100.005357]        tcp_check_req+0x517/0x5f1
[  100.005927]        tcp_v4_rcv+0x6ad/0xce7
[  100.006472]        ip_local_deliver_finish+0x1d4/0x281
[  100.007153]        ip_local_deliver+0xaf/0xcf
[  100.007736]        ip_rcv_finish+0x632/0x6ff
[  100.008311]        ip_rcv+0x45d/0x4a6
[  100.008804]        __netif_receive_skb_core+0x588/0x9b0
[  100.009514]        __netif_receive_skb+0x32/0xc5
[  100.010130]        netif_receive_skb_internal+0x66/0x14d
[  100.010839]        napi_gro_receive+0x148/0x205
[  100.011454]        receive_buf+0xfa5/0xfb7
[  100.012001]        virtnet_poll+0x1f0/0x2e4
[  100.012559]        net_rx_action+0x178/0x3c6
[  100.013135]        __do_softirq+0x215/0x555
[  100.013690]        irq_exit+0x71/0xd6
[  100.014182]        do_IRQ+0xe2/0xfa
[  100.014660]        ret_from_intr+0x0/0x1e
[  100.015195]        native_safe_halt+0x6/0x8
[  100.015749]        default_idle+0x24/0x37
[  100.016291]        arch_cpu_idle+0xf/0x11
[  100.016828]        default_idle_call+0x28/0x2f
[  100.017418]        do_idle+0xf5/0x190
[  100.017911]        cpu_startup_entry+0x1f/0x21
[  100.018504]        start_secondary+0x186/0x18c
[  100.019102]        verify_cpu+0x0/0xf1
[  100.019617]
-> #0 (slock-AF_INET){+.-.}:
[  100.020342]        __lock_acquire+0x1168/0x14c5
[  100.020951]        lock_acquire+0x154/0x220
[  100.021512]        _raw_spin_lock+0x34/0x6a
[  100.022078]        tcp_delack_timer+0x29/0xb1
[  100.022672]        call_timer_fn+0x139/0x36b
[  100.023250]        __run_timers.part.35+0x2c2/0x2f7
[  100.023899]        run_timer_softirq+0x52/0x9f
[  100.024493]        __do_softirq+0x215/0x555
[  100.025048]        irq_exit+0x71/0xd6
[  100.025546]        smp_apic_timer_interrupt+0x235/0x32a
[  100.026246]        apic_timer_interrupt+0x9d/0xb0
[  100.026875]        native_safe_halt+0x6/0x8
[  100.027435]        default_idle+0x24/0x37
[  100.027974]        arch_cpu_idle+0xf/0x11
[  100.028512]        default_idle_call+0x28/0x2f
[  100.029109]        do_idle+0xf5/0x190
[  100.029598]        cpu_startup_entry+0x1f/0x21
[  100.030198]        start_secondary+0x186/0x18c
[  100.030790]        verify_cpu+0x0/0xf1
[  100.031290]
other info that might help us debug this:

[  100.032339]  Possible unsafe locking scenario:

[  100.033125]        CPU0                    CPU1
[  100.033722]        ----                    ----
[  100.034335]   lock((timer));
[  100.034728]                                lock(slock-AF_INET);
[  100.035513]                                lock((timer));
[  100.036233]   lock(slock-AF_INET);
[  100.036695]
 *** DEADLOCK ***

[  100.037487] 1 lock held by swapper/1/0:
[  100.037996]  #0:  ((timer)){+.-.}, at: [<ffffffff810f3c0b>]
call_timer_fn+0x5/0x36b
[  100.039008]
stack backtrace:
[  100.039586] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.14.0-rc7+ #23
[  100.040434] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[  100.041757] Call Trace:
[  100.042090]  <IRQ>
[  100.042381]  dump_stack+0x81/0xb6
[  100.042831]  print_circular_bug.isra.39+0x22e/0x23c
[  100.043483]  __lock_acquire+0x1168/0x14c5
[  100.044023]  ? mark_lock+0x3a/0x265
[  100.044504]  lock_acquire+0x154/0x220
[  100.045003]  ? lock_acquire+0x154/0x220
[  100.045525]  ? tcp_delack_timer+0x29/0xb1
[  100.046061]  ? tcp_delack_timer_handler+0x1c0/0x1c0
[  100.046719]  _raw_spin_lock+0x34/0x6a
[  100.047211]  ? tcp_delack_timer+0x29/0xb1
[  100.047751]  tcp_delack_timer+0x29/0xb1
[  100.048274]  ? tcp_delack_timer_handler+0x1c0/0x1c0
[  100.048921]  call_timer_fn+0x139/0x36b
[  100.049436]  __run_timers.part.35+0x2c2/0x2f7
[  100.050023]  ? tcp_delack_timer_handler+0x1c0/0x1c0
[  100.050678]  ? kvm_clock_read+0x25/0x2e
[  100.051194]  ? kvm_clock_get_cycles+0x9/0xb
[  100.051753]  ? lock_is_held_type+0x103/0x112
[  100.052328]  run_timer_softirq+0x52/0x9f
[  100.052853]  __do_softirq+0x215/0x555
[  100.053347]  irq_exit+0x71/0xd6
[  100.053794]  smp_apic_timer_interrupt+0x235/0x32a
[  100.054426]  apic_timer_interrupt+0x9d/0xb0
[  100.054993]  </IRQ>
[  100.055287] RIP: 0010:native_safe_halt+0x6/0x8
[  100.055880] RSP: 0018:ffff880035fafea0 EFLAGS: 00000246 ORIG_RAX:
ffffffffffffff10
[  100.056872] RAX: 1ffff10006bf3d00 RBX: 0000000000000000 RCX:
ffffffff810cae10
[  100.057810] RDX: 1ffffffff03e3e31 RSI: 0000000000000007 RDI:
ffff880035f9eafc
[  100.058757] RBP: ffff880035fafea0 R08: dffffc0000000000 R09:
0000000000000001
[  100.059685] R10: fffffbfff03e4188 R11: ffffffff81f20c3b R12:
0000000000000000
[  100.060619] R13: ffff880035f9e300 R14: ffff880035f9e300 R15:
ffff880035f9e300
[  100.061556]  ? trace_hardirqs_on_caller+0x22e/0x274
[  100.062216]  default_idle+0x24/0x37
[  100.062687]  arch_cpu_idle+0xf/0x11
[  100.063159]  default_idle_call+0x28/0x2f
[  100.063691]  do_idle+0xf5/0x190
[  100.064120]  cpu_startup_entry+0x1f/0x21
[  100.064643]  start_secondary+0x186/0x18c
[  100.065168]  secondary_startup_64+0xa5/0xa5
[  115.194378] nr_pdflush_threads exported in /proc is scheduled for removal