[llvm] r291216 - [Orc][RPC] Fix an obvious locking-order bug in RawByteChannel::startSendMessage.

[Lang Hames via llvm-commits]

Author: lhames
Date: Fri Jan  6 00:22:31 2017
New Revision: 291216

URL: http://llvm.org/viewvc/llvm-project?rev=291216&view=rev
Log:
[Orc][RPC] Fix an obvious locking-order bug in RawByteChannel::startSendMessage.

The lock needs to be acquired before the data is sent, not afterwards. This
think-o slipped in during the refactor in r286620, but went unnoticed as the
resulting bug only manifests in multi-threaded clients (of which there are none
in-tree).

No unit test as the bug depends on thread scheduling.


Modified:
    llvm/trunk/include/llvm/ExecutionEngine/Orc/RawByteChannel.h

Modified: llvm/trunk/include/llvm/ExecutionEngine/Orc/RawByteChannel.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ExecutionEngine/Orc/RawByteChannel.h?rev=291216&r1=291215&r2=291216&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ExecutionEngine/Orc/RawByteChannel.h (original)
+++ llvm/trunk/include/llvm/ExecutionEngine/Orc/RawByteChannel.h Fri Jan  6 00:22:31 2017
@@ -47,9 +47,9 @@ public:
   /// Locks the channel for writing.
   template <typename FunctionIdT, typename SequenceIdT>
   Error startSendMessage(const FunctionIdT &FnId, const SequenceIdT &SeqNo) {
+    writeLock.lock();
     if (auto Err = serializeSeq(*this, FnId, SeqNo))
       return Err;
-    writeLock.lock();
     return Error::success();
   }