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, 16 insertions, 0 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 9abbe630c456..8c9b7a1c4138 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -248,6 +248,9 @@ struct ftrace_event_call {
 #ifdef CONFIG_PERF_EVENTS
         int                             perf_refcount;
         struct hlist_head __percpu      *perf_events;
+
+        int     (*perf_perm)(struct ftrace_event_call *,
+                             struct perf_event *);
 #endif
 };
 
@@ -317,6 +320,19 @@ struct ftrace_event_file {
         }                                                               \
         early_initcall(trace_init_flags_##name);
 
+#define __TRACE_EVENT_PERF_PERM(name, expr...)                          \
+        static int perf_perm_##name(struct ftrace_event_call *tp_event, \
+                                    struct perf_event *p_event)         \
+        {                                                               \
+                return ({ expr; });                                     \
+        }                                                               \
+        static int __init trace_init_perf_perm_##name(void)             \
+        {                                                               \
+                event_##name.perf_perm = &perf_perm_##name;             \
+                return 0;                                               \
+        }                                                               \
+        early_initcall(trace_init_perf_perm_##name);
+
 #define PERF_MAX_TRACE_SIZE     2048
 
 #define MAX_FILTER_STR_VAL      256     /* Should handle KSYM_SYMBOL_LEN */