Debug failure in SafeAccess::load

Author: jbachorik

ddprof-lib/src/main/cpp/ctimer_linux.cpp

@@ -20,6 +20,7 @@
 #include "debugSupport.h"
 #include "profiler.h"
 #include "vmStructs.h"
+#include <assert.h>
 #include <stdlib.h>
 #include <sys/syscall.h>
 #include <time.h>
@@ -202,6 +203,7 @@ void CTimer::signalHandler(int signo, siginfo_t *siginfo, void *ucontext) {
     return;
   int tid = 0;
   ProfiledThread *current = ProfiledThread::current();
+  assert(current == nullptr || !current->isDeepCrashHandler());
   if (current != NULL) {
     current->noteCPUSample(Profiler::instance()->recordingEpoch());
     tid = current->tid();

ddprof-lib/src/main/cpp/thread.h

@@ -4,6 +4,7 @@
 #include "os.h"
 #include "threadLocalData.h"
 #include <atomic>
+#include <cstdint>
 #include <jvmti.h>
 #include <pthread.h>
 #include <stdlib.h>
@@ -12,6 +13,13 @@
 
 class ProfiledThread : public ThreadLocalData {
 private:
+  // We are allowing several levels of nesting because we can be
+  // eg. in a crash handler when wallclock signal kicks in,
+  // catching sigseg while also triggering CPU signal handler
+  // which would also potentially trigger sigseg we need to handle.
+  // This means 3 levels but we allow for some wiggling space, just in case.
+  // Even with 5 levels cap we will need any highly recursing signal handlers
+  static constexpr u32 CRASH_HANDLER_NESTING_LIMIT = 5;
   static pthread_key_t _tls_key;
   static int _buffer_size;
   static std::atomic<int> _running_buffer_pos;
@@ -81,17 +89,21 @@ class ProfiledThread : public ThreadLocalData {
   // this is called in the crash handler to avoid recursing
   bool enterCrashHandler() {
     u32 prev = _crash_depth;
-    // this is thread local; no need for atomic cmpxchg
-    if (prev == 0) {
-      _crash_depth = 1;
+    // This is thread local; no need for atomic cmpxchg
+    if (prev < CRASH_HANDLER_NESTING_LIMIT) {
+      _crash_depth++;
       return true;
     }
     return false;
   }
 
   // needs to be called when the crash handler exits
   void exitCrashHandler() {
-    _crash_depth = 0;
+    _crash_depth--;
+  }
+
+  bool isDeepCrashHandler() {
+    return _crash_depth > CRASH_HANDLER_NESTING_LIMIT;
   }
 
   static void signalHandler(int signo, siginfo_t *siginfo, void *ucontext);