[Exclusivity] Fix insertion/remove in AccessSet in runtime.

stdlib/public/runtime/Exclusivity.cpp

@@ -69,6 +69,11 @@ struct Access {
   Access **getHere() const {
     return reinterpret_cast<Access**>(HereAndAction & HereMask);
   }
+
+  void setHere(Access **newHere) {
+    HereAndAction = reinterpret_cast<uintptr_t>(newHere) | uintptr_t(getAccessAction());
+  }
+
   ExclusivityFlags getAccessAction() const {
     return ExclusivityFlags(HereAndAction & ActionMask);
   }
@@ -114,10 +119,14 @@ class AccessSet {
     }
 
     access->initialize(pointer, curP, action);
+    *curP = access;
   }
 
   static void remove(Access *access) {
-    *access->getHere() = access->Next;
+    Access **here = access->getHere();
+    *here = access->Next;
+    if (access->Next != nullptr)
+      access->Next->setHere(here);
   }
 };
 

test/Interpreter/enforce_exclusive_access.swift

@@ -0,0 +1,114 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: %target-build-swift %s -o %t/a.out -enforce-exclusivity=checked
+//
+// RUN: %target-run %t/a.out
+// REQUIRES: executable_test
+
+// Tests for traps at run time when enforcing exclusive access.
+
+import StdlibUnittest
+
+struct X {
+  var i = 7
+}
+
+/// Calling this function will begin a read access to the variable referred to
+/// in the first parameter that lasts for the duration of the call. Any
+/// accesses in the closure will therefore be nested inside the outer read.
+func readAndPerform<T>(_ _: UnsafePointer<T>, closure: () ->()) {
+  closure()
+}
+
+/// Begin a modify access to the first paraemter and call the closure inside it.
+func modifyAndPerform<T>(_ _: UnsafeMutablePointer<T>, closure: () ->()) {
+  closure()
+}
+
+var globalX = X()
+
+var ExclusiveAccessTestSuite = TestSuite("ExclusiveAccess")
+
+ExclusiveAccessTestSuite.test("Read") {
+  let l = globalX // no-trap
+  _blackHole(l)
+}
+
+// It is safe for a read access to overlap with a read.
+ExclusiveAccessTestSuite.test("ReadInsideRead") {
+  readAndPerform(&globalX) {
+    let l = globalX // no-trap
+    _blackHole(l)
+  }
+}
+
+ExclusiveAccessTestSuite.test("ModifyInsideRead")
+  .skip(.custom(
+    { _isFastAssertConfiguration() },
+    reason: "this trap is not guaranteed to happen in -Ounchecked"))
+  .crashOutputMatches("modify/read access conflict detected on address")
+  .code
+{
+  readAndPerform(&globalX) {
+    expectCrashLater()
+    globalX = X()
+  }
+}
+
+ExclusiveAccessTestSuite.test("ReadInsideModify")
+  .skip(.custom(
+    { _isFastAssertConfiguration() },
+    reason: "this trap is not guaranteed to happen in -Ounchecked"))
+  .crashOutputMatches("read/modify access conflict detected on address")
+  .code
+{
+  modifyAndPerform(&globalX) {
+    expectCrashLater()
+    let l = globalX
+    _blackHole(l)
+  }
+}
+
+ExclusiveAccessTestSuite.test("ModifyInsideModify")
+  .skip(.custom(
+    { _isFastAssertConfiguration() },
+    reason: "this trap is not guaranteed to happen in -Ounchecked"))
+  .crashOutputMatches("modify/modify access conflict detected on address")
+  .code
+{
+  modifyAndPerform(&globalX) {
+    expectCrashLater()
+    globalX.i = 12
+  }
+}
+
+var globalOtherX = X()
+
+// It is safe for two modifications of different variables
+// to overlap.
+ExclusiveAccessTestSuite.test("ModifyInsideModifyOfOther") {
+  modifyAndPerform(&globalOtherX) {
+    globalX.i = 12 // no-trap
+  }
+}
+
+// The access durations for these two modifications do not overlap
+ExclusiveAccessTestSuite.test("ModifyFollowedByModify") {
+  globalX = X()
+  _blackHole(())
+
+  globalX = X() // no-trap
+}
+
+ExclusiveAccessTestSuite.test("ClosureCaptureModifyModify") {
+  var x = X()
+  modifyAndPerform(&x) {
+    // FIXME: This should be caught dynamically.
+    x.i = 12
+  }
+}
+
+
+
+
+runAllTests()