[PATCH] D31356: [Support] Avoid concurrency hazard in signal handler registration

[Bruno Cardoso Lopes via Phabricator via llvm-commits]

bruno created this revision.

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. Since there are a few potentially affected static functions, this patch fix `RegisterHandlers` to use a mutex.


https://reviews.llvm.org/D31356

Files:
  lib/Support/Unix/Signals.inc


Index: lib/Support/Unix/Signals.inc
===================================================================
--- lib/Support/Unix/Signals.inc
+++ lib/Support/Unix/Signals.inc
@@ -149,11 +149,7 @@
 #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;


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