8364501: Compiler shutdown crashes on access to deleted CompileTask

Reviewed-by: kvn, mhaessig

src/hotspot/share/compiler/compileBroker.cpp

@@ -371,6 +371,7 @@ void CompileQueue::delete_all() {
 
   // Iterate over all tasks in the compile queue
   while (current != nullptr) {
+    CompileTask* next = current->next();
     if (!current->is_blocking()) {
       // Non-blocking task. No one is waiting for it, delete it now.
       delete current;
@@ -379,7 +380,7 @@ void CompileQueue::delete_all() {
       // to delete the task. We cannot delete it here, because we do not
       // coordinate with waiters. We will notify the waiters later.
     }
-    current = current->next();
+    current = next;
   }
   _first = nullptr;
   _last = nullptr;
@@ -504,6 +505,8 @@ void CompileQueue::remove(CompileTask* task) {
     assert(task == _last, "Sanity");
     _last = task->prev();
   }
+  task->set_next(nullptr);
+  task->set_prev(nullptr);
   --_size;
   ++_total_removed;
 }
@@ -1728,17 +1731,22 @@ void CompileBroker::wait_for_completion(CompileTask* task) {
 
   // It is harmless to check this status without the lock, because
   // completion is a stable property.
-  if (!task->is_complete() && is_compilation_disabled_forever()) {
-    // Task is not complete, and we are exiting for compilation shutdown.
-    // The task can still be executed by some compiler thread, therefore
-    // we cannot delete it. This will leave task allocated, which leaks it.
-    // At this (degraded) point, it is less risky to abandon the task,
-    // rather than attempting a more complicated deletion protocol.
+  if (!task->is_complete()) {
+    // Task is not complete, likely because we are exiting for compilation
+    // shutdown. The task can still be reached through the queue, or executed
+    // by some compiler thread. There is no coordination with either MCQ lock
+    // holders or compilers, therefore we cannot delete the task.
+    //
+    // This will leave task allocated, which leaks it. At this (degraded) point,
+    // it is less risky to abandon the task, rather than attempting a more
+    // complicated deletion protocol.
     free_task = false;
   }
 
   if (free_task) {
     assert(task->is_complete(), "Compilation should have completed");
+    assert(task->next() == nullptr && task->prev() == nullptr,
+           "Completed task should not be in the queue");
 
     // By convention, the waiter is responsible for deleting a
     // blocking CompileTask. Since there is only one waiter ever

src/hotspot/share/compiler/compileTask.cpp

@@ -74,6 +74,7 @@ CompileTask::CompileTask(int compile_id,
   _arena_bytes = 0;
 
   _next = nullptr;
+  _prev = nullptr;
 
   Atomic::add(&_active_tasks, 1, memory_order_relaxed);
 }

src/hotspot/share/compiler/compileTask.hpp

@@ -101,7 +101,8 @@ class CompileTask : public CHeapObj<mtCompiler> {
 #endif
   int                  _comp_level;
   int                  _num_inlined_bytecodes;
-  CompileTask*         _next, *_prev;
+  CompileTask*         _next;
+  CompileTask*         _prev;
   // Fields used for logging why the compilation was initiated:
   jlong                _time_queued;  // time when task was enqueued
   jlong                _time_started; // time when compilation started