perf: fuzzer WARNING event_function_local.constprop

[Vince Weaver]

Got this while fuzzing on the Haswell machine.  It's relatively repeatable 
if anyone wants me to chase it down more.

It maps to
	int ret = event_function(&efs);
	WARN_ON_ONCE(ret);
In event_function_local()

[166817.446302] ------------[ cut here ]------------
[166817.451347] WARNING: CPU: 1 PID: 0 at kernel/events/core.c:254 event_function_local.constprop.106+0x4c/0x50
[166817.535510] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0-rc1+ #187
[166817.542500] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS 01/26/2014
[166817.550535]  0000000000000000 ffff88011ea43ca8 ffffffff81437641 0000000000000000
[166817.558676]  0000000000000000 ffff88011ea43ce8 ffffffff81076bab 000000fe8116864d
[166817.566785]  0000000000000002 0000000000014000 ffff8800ac3ae3e8 ffff8800ac3ae000
[166817.574918] Call Trace:
[166817.577654]  <IRQ>  [<ffffffff81437641>] dump_stack+0x63/0x82
[166817.583957]  [<ffffffff81076bab>] __warn+0xcb/0xf0
[166817.589185]  [<ffffffff81076c9d>] warn_slowpath_null+0x1d/0x20
[166817.595550]  [<ffffffff8116bbac>] event_function_local.constprop.106+0x4c/0x50
[166817.603398]  [<ffffffff8116e3a0>] ? task_ctx_sched_out+0x50/0x50
[166817.609948]  [<ffffffff81174c71>] perf_pending_event+0xd1/0xe0
[166817.616291]  [<ffffffff8115dea8>] irq_work_run_list+0x48/0x70
[166817.622566]  [<ffffffff8115dee8>] irq_work_run+0x18/0x40
[166817.628357]  [<ffffffff81032cee>] smp_irq_work_interrupt+0x2e/0x40
[166817.635090]  [<ffffffff81723a02>] irq_work_interrupt+0x82/0x90
[166817.641445]  [<ffffffff81721b81>] ? _raw_spin_unlock_irqrestore+0x31/0x40
[166817.648822]  [<ffffffff810bb9b2>] complete+0x42/0x50
[166817.654231]  [<ffffffff810df8f0>] ? trace_raw_output_rcu_utilization+0x60/0x60
[166817.662107]  [<ffffffff810df902>] wakeme_after_rcu+0x12/0x20
[166817.668302]  [<ffffffff810e3aa5>] rcu_process_callbacks+0x2f5/0x6a0
[166817.675140]  [<ffffffff810e3a3f>] ? rcu_process_callbacks+0x28f/0x6a0
[166817.682143]  [<ffffffff81724c83>] __do_softirq+0x113/0x2c6
[166817.688121]  [<ffffffff8107ca53>] irq_exit+0xa3/0xb0
[166817.693553]  [<ffffffff81724a42>] smp_apic_timer_interrupt+0x42/0x50
[166817.700467]  [<ffffffff81722da2>] apic_timer_interrupt+0x82/0x90
[166817.706980]  <EOI>  [<ffffffff815ad21b>] ? cpuidle_enter_state+0x12b/0x2d0
[166817.714482]  [<ffffffff815ad3f7>] cpuidle_enter+0x17/0x20
[166817.720354]  [<ffffffff810bbada>] call_cpuidle+0x2a/0x50
[166817.726144]  [<ffffffff810bbeaf>] cpu_startup_entry+0x28f/0x340
[166817.732587]  [<ffffffff8104fda3>] start_secondary+0x133/0x140
[166817.738867] ---[ end trace 05ef6c9af3dc0e24 ]---