[llvm] r298871 - [Support] Avoid concurrency hazard in signal handler registration

[Bruno Cardoso Lopes via llvm-commits]

Author: bruno
Date: Mon Mar 27 13:21:31 2017
New Revision: 298871

URL: http://llvm.org/viewvc/llvm-project?rev=298871&view=rev
Log:
[Support] Avoid concurrency hazard in signal handler registration

Several static functions from the signal API can be invoked
simultaneously; RemoveFileOnSignal for instance can be called indirectly
by multiple parallel loadModule() invocations, which might lead to
the assertion:

Assertion failed: (NumRegisteredSignals < array_lengthof(RegisteredSignalInfo) && "Out of space for signal handlers!"),
  function RegisterHandler, file /llvm/lib/Support/Unix/Signals.inc, line 105.

RemoveFileOnSignal calls RegisterHandlers(), which isn't currently
mutex protected, leading to the behavior above. This potentially affect
a few other users of RegisterHandlers() too.

rdar://problem/30381224

Modified:
    llvm/trunk/lib/Support/Unix/Signals.inc

Modified: llvm/trunk/lib/Support/Unix/Signals.inc
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Unix/Signals.inc?rev=298871&r1=298870&r2=298871&view=diff
==============================================================================
--- llvm/trunk/lib/Support/Unix/Signals.inc (original)
+++ llvm/trunk/lib/Support/Unix/Signals.inc Mon Mar 27 13:21:31 2017
@@ -149,11 +149,7 @@ static void CreateSigAltStack() {}
 #endif
 
 static void RegisterHandlers() {
-  // We need to dereference the signals mutex during handler registration so
-  // that we force its construction. This is to prevent the first use being
-  // during handling an actual signal because you can't safely call new in a
-  // signal handler.
-  *SignalsMutex;
+  sys::SmartScopedLock<true> Guard(*SignalsMutex);
 
   // If the handlers are already registered, we're done.
   if (NumRegisteredSignals != 0) return;