Add a StackTraceTimeout option to set the timeout for the backtrace h…

…andler.

Summary: This specifies the maximum number of seconds spent for generating a stack trace
when hhvm is crashed. The default is 0 which means no timeout. This can be set
to prevent from deadlocks in the backtrace handler.

Part of #4533 and #2408.
Closes #4828

Reviewed By: @markw65

Differential Revision: D1844818

Pulled By: @fredemmott

hphp/doc/options.compiled

@@ -595,6 +595,8 @@ next requests.
     CoreDumpEmail = email address
     CoreDumpReport = true
     CoreDumpReportDirectory = /tmp
+
+    StackTraceTimeout = 0
   }
 
 - FullBacktrace, ServerErrorMessage, TranslateSource
@@ -612,6 +614,12 @@ file's location. ClearInputOnSuccess can automatically delete requests that
 had 200 responses and it's useful to capture 500 errors on production without
 capturing good responses.
 
+- StackTraceTimeout
+
+This specifies the maximum number of seconds spent for generating a stack trace
+when hhvm is crashed. The default is 0 which means no timeout. This can be set
+to prevent from deadlocks in the backtrace handler.
+
 - APCSize
 
 There are options for APC size profiling. If enabled, APC overall size will be

hphp/runtime/base/crash-reporter.cpp

@@ -31,6 +31,17 @@ namespace HPHP {
 bool IsCrashing = false;
 
 static void bt_handler(int sig) {
+  if (RuntimeOption::StackTraceTimeout > 0) {
+    if (IsCrashing && sig == SIGALRM) {
+      // Raising the previous signal does not terminate the program.
+      signal(SIGABRT, SIG_DFL);
+      abort();
+    } else {
+      signal(SIGALRM, bt_handler);
+      alarm(RuntimeOption::StackTraceTimeout);
+    }
+  }
+
   // In case we crash again in the signal hander or something
   signal(sig, SIG_DFL);
   IsCrashing = true;

hphp/runtime/base/runtime-option.cpp

@@ -309,6 +309,7 @@ bool RuntimeOption::CoreDumpReport = true;
 std::string RuntimeOption::StackTraceFilename;
 bool RuntimeOption::LocalMemcache = false;
 bool RuntimeOption::MemcacheReadOnly = false;
+int RuntimeOption::StackTraceTimeout = 0; // seconds; 0 means unlimited
 
 bool RuntimeOption::EnableStats = false;
 bool RuntimeOption::EnableAPCStats = false;
@@ -1409,6 +1410,7 @@ void RuntimeOption::Load(IniSetting::Map& ini, Hdf& config,
 
     Config::Bind(LocalMemcache, ini, debug["LocalMemcache"]);
     Config::Bind(MemcacheReadOnly, ini, debug["MemcacheReadOnly"]);
+    Config::Bind(StackTraceTimeout, ini, debug["StackTraceTimeout"], 0);
 
     {
       Hdf simpleCounter = debug["SimpleCounter"];

hphp/runtime/base/runtime-option.h

@@ -293,6 +293,7 @@ class RuntimeOption {
   static std::string StackTraceFilename;
   static bool LocalMemcache;
   static bool MemcacheReadOnly;
+  static int StackTraceTimeout;
 
   static bool EnableStats;
   static bool EnableAPCStats;