ftrace, perf: Avoid infinite event generation loop

Vince's perf-trinity fuzzer found yet another 'interesting' problem.

When we sample the irq_work_exit tracepoint with period==1 (or
PERF_SAMPLE_PERIOD) and we add an fasync SIGNAL handler we create an
infinite event generation loop:

  ,-> <IPI>
  |     irq_work_exit() ->
  |       trace_irq_work_exit() ->
  |         ...
  |           __perf_event_overflow() -> (due to fasync)
  |             irq_work_queue() -> (irq_work_list must be empty)
  '---------      arch_irq_work_raise()

Similar things can happen due to regular poll() wakeups if we exceed
the ring-buffer wakeup watermark, or have an event_limit.

To avoid this, dis-allow sampling this particular tracepoint.

In order to achieve this, create a special perf_perm function pointer
for each event and call this (when set) on trying to create a
tracepoint perf event.

[ roasted: use expr... to allow for ',' in your expression ]

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20131114152304.GC5364@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/include/asm/trace/irq_vectors.h b/arch/x86/include/asm/trace/irq_vectors.h
index 2874df24e7a4..4cab890007a7 100644
--- a/arch/x86/include/asm/trace/irq_vectors.h
+++ b/arch/x86/include/asm/trace/irq_vectors.h
@@ -72,6 +72,17 @@ DEFINE_IRQ_VECTOR_EVENT(x86_platform_ipi);
 DEFINE_IRQ_VECTOR_EVENT(irq_work);
 
 /*
+ * We must dis-allow sampling irq_work_exit() because perf event sampling
+ * itself can cause irq_work, which would lead to an infinite loop;
+ *
+ *  1) irq_work_exit happens
+ *  2) generates perf sample
+ *  3) generates irq_work
+ *  4) goto 1
+ */
+TRACE_EVENT_PERF_PERM(irq_work_exit, is_sampling_event(p_event) ? -EPERM : 0);
+
+/*
  * call_function - called when entering/exiting a call function interrupt
  * vector handler
  */