STM.c:stmCommitNestedTransaction bogosity

there is a superfluous if (result) in stmCommitNestedTransaction in STM.c. as a consequence, if check_read_only returns non-zero, revert_ownership will not be called, which means that when the transaction is restarted and reads a variable, that TVar will still be locked by the previous attempt, resulting in an infinite loop in readTVar.

here is a patch (against ghc 6.6 darcs checked out on 2007-02-18).

--- /home/ms/www/ghc/rts/STM.c	2007-02-18 19:52:42.000000000 +0100
+++ ./STM.c	2007-03-02 23:27:53.000000000 +0100
@@ -1013,7 +1013,6 @@
       // at the end of the call to validate_and_acquire_ownership.  This forms the
       // linearization point of the commit.
 
-      if (result) {
         TRACE("%p : read-check succeeded\n", trec);
         FOR_EACH_ENTRY(trec, e, {
           // Merge each entry into the enclosing transaction record, release all
@@ -1027,9 +1026,8 @@
           merge_update_into(cap, et, s, e -> expected_value, e -> new_value);
           ACQ_ASSERT(s -> current_value != (StgClosure *)trec);
         });
-      } else {
+    } else {
         revert_ownership(trec, FALSE);
-      }
     }
   } 

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Multiple
Architecture	Multiple