On Mon, Aug 13, 2018 at 05:55:02PM -0700, syzbot wrote:

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 7203 at lib/refcount.c:187
refcount_sub_and_test+0x2e7/0x350 lib/refcount.c:187
Kernel panic - not syncing: panic_on_warn set ...

...

 refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212
 sctp_transport_put+0x76/0x200 net/sctp/transport.c:331
 sctp_generate_heartbeat_event+0x2d7/0x450 net/sctp/sm_sideeffect.c:416
 call_timer_fn+0x242/0x970 kernel/time/timer.c:1326
 expire_timers kernel/time/timer.c:1363 [inline]
 __run_timers+0x7a6/0xc70 kernel/time/timer.c:1666
 run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
 __do_softirq+0x2e8/0xb17 kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:372 [inline]
 irq_exit+0x1d4/0x210 kernel/softirq.c:412
 exiting_irq arch/x86/include/asm/apic.h:527 [inline]
 smp_apic_timer_interrupt+0x186/0x730 arch/x86/kernel/apic/apic.c:1055
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
 </IRQ>

Interesting, again on heartbeat timer handler.

  Marcelo