Title: [236382] trunk
Revision
236382
Author
[email protected]
Date
2018-09-22 00:28:39 -0700 (Sat, 22 Sep 2018)

Log Message

The sampling should not use Strong<CodeBlock> in its machineLocation field
https://bugs.webkit.org/show_bug.cgi?id=189319

Reviewed by Filip Pizlo.

JSTests:

* stress/sampling-profiler-richards.js: Added.

Source/_javascript_Core:

The sampling profiler has a CLI mode where we gather information about inline
call frames. That data structure was using a Strong<CodeBlock>. We were
constructing this Strong<CodeBlock> during GC concurrently to processing all
the Strong handles. This is a bug since we end up corrupting that data
structure. This patch fixes this by just making this data structure use the
sampling profiler's mechanism for holding onto and properly visiting heap pointers.

* inspector/agents/InspectorScriptProfilerAgent.cpp:
(Inspector::InspectorScriptProfilerAgent::trackingComplete):
* runtime/SamplingProfiler.cpp:
(JSC::SamplingProfiler::processUnverifiedStackTraces):

(JSC::SamplingProfiler::reportTopFunctions):
(JSC::SamplingProfiler::reportTopBytecodes):
These CLI helpers needed a DeferGC otherwise we may end up deadlocking when we
cause a GC to happen while already holding the sampling profiler's
lock.

Modified Paths

Added Paths

Diff

Modified: trunk/JSTests/ChangeLog (236381 => 236382)


--- trunk/JSTests/ChangeLog	2018-09-22 05:26:44 UTC (rev 236381)
+++ trunk/JSTests/ChangeLog	2018-09-22 07:28:39 UTC (rev 236382)
@@ -1,3 +1,12 @@
+2018-09-22  Saam barati  <[email protected]>
+
+        The sampling should not use Strong<CodeBlock> in its machineLocation field
+        https://bugs.webkit.org/show_bug.cgi?id=189319
+
+        Reviewed by Filip Pizlo.
+
+        * stress/sampling-profiler-richards.js: Added.
+
 2018-09-19  Yusuke Suzuki  <[email protected]>
 
         [JSC] Optimize Array#indexOf in C++ runtime

Added: trunk/JSTests/stress/sampling-profiler-richards.js (0 => 236382)


--- trunk/JSTests/stress/sampling-profiler-richards.js	                        (rev 0)
+++ trunk/JSTests/stress/sampling-profiler-richards.js	2018-09-22 07:28:39 UTC (rev 236382)
@@ -0,0 +1,541 @@
+//@ runDefault("--collectContinuously=1", "--useSamplingProfiler=1", "--collectSamplingProfilerDataForJSCShell=1")
+
+"use strict";
+
+// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+// This is a _javascript_ implementation of the Richards
+// benchmark from:
+//
+//    http://www.cl.cam.ac.uk/~mr10/Bench.html
+//
+// The benchmark was originally implemented in BCPL by
+// Martin Richards.
+
+
+/**
+ * The Richards benchmark simulates the task dispatcher of an
+ * operating system.
+ **/
+function runRichards() {
+  var scheduler = new Scheduler();
+  scheduler.addIdleTask(ID_IDLE, 0, null, COUNT);
+
+  var queue = new Packet(null, ID_WORKER, KIND_WORK);
+  queue = new Packet(queue,  ID_WORKER, KIND_WORK);
+  scheduler.addWorkerTask(ID_WORKER, 1000, queue);
+
+  queue = new Packet(null, ID_DEVICE_A, KIND_DEVICE);
+  queue = new Packet(queue,  ID_DEVICE_A, KIND_DEVICE);
+  queue = new Packet(queue,  ID_DEVICE_A, KIND_DEVICE);
+  scheduler.addHandlerTask(ID_HANDLER_A, 2000, queue);
+
+  queue = new Packet(null, ID_DEVICE_B, KIND_DEVICE);
+  queue = new Packet(queue,  ID_DEVICE_B, KIND_DEVICE);
+  queue = new Packet(queue,  ID_DEVICE_B, KIND_DEVICE);
+  scheduler.addHandlerTask(ID_HANDLER_B, 3000, queue);
+
+  scheduler.addDeviceTask(ID_DEVICE_A, 4000, null);
+
+  scheduler.addDeviceTask(ID_DEVICE_B, 5000, null);
+
+  scheduler.schedule();
+
+  if (scheduler.queueCount != EXPECTED_QUEUE_COUNT ||
+      scheduler.holdCount != EXPECTED_HOLD_COUNT) {
+    var msg =
+        "Error during execution: queueCount = " + scheduler.queueCount +
+        ", holdCount = " + scheduler.holdCount + ".";
+    throw new Error(msg);
+  }
+}
+
+var COUNT = 1000;
+
+/**
+ * These two constants specify how many times a packet is queued and
+ * how many times a task is put on hold in a correct run of richards.
+ * They don't have any meaning a such but are characteristic of a
+ * correct run so if the actual queue or hold count is different from
+ * the expected there must be a bug in the implementation.
+ **/
+var EXPECTED_QUEUE_COUNT = 2322;
+var EXPECTED_HOLD_COUNT = 928;
+
+
+/**
+ * A scheduler can be used to schedule a set of tasks based on their relative
+ * priorities.  Scheduling is done by maintaining a list of task control blocks
+ * which holds tasks and the data queue they are processing.
+ * @constructor
+ */
+function Scheduler() {
+  this.queueCount = 0;
+  this.holdCount = 0;
+  this.blocks = new Array(NUMBER_OF_IDS);
+  this.list = null;
+  this.currentTcb = null;
+  this.currentId = null;
+}
+
+var ID_IDLE       = 0;
+var ID_WORKER     = 1;
+var ID_HANDLER_A  = 2;
+var ID_HANDLER_B  = 3;
+var ID_DEVICE_A   = 4;
+var ID_DEVICE_B   = 5;
+var NUMBER_OF_IDS = 6;
+
+var KIND_DEVICE   = 0;
+var KIND_WORK     = 1;
+
+/**
+ * Add an idle task to this scheduler.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ * @param {int} count the number of times to schedule the task
+ */
+Scheduler.prototype.addIdleTask = function (id, priority, queue, count) {
+  this.addRunningTask(id, priority, queue, new IdleTask(this, 1, count));
+};
+
+/**
+ * Add a work task to this scheduler.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ */
+Scheduler.prototype.addWorkerTask = function (id, priority, queue) {
+  this.addTask(id, priority, queue, new WorkerTask(this, ID_HANDLER_A, 0));
+};
+
+/**
+ * Add a handler task to this scheduler.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ */
+Scheduler.prototype.addHandlerTask = function (id, priority, queue) {
+  this.addTask(id, priority, queue, new HandlerTask(this));
+};
+
+/**
+ * Add a handler task to this scheduler.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ */
+Scheduler.prototype.addDeviceTask = function (id, priority, queue) {
+  this.addTask(id, priority, queue, new DeviceTask(this))
+};
+
+/**
+ * Add the specified task and mark it as running.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ * @param {Task} task the task to add
+ */
+Scheduler.prototype.addRunningTask = function (id, priority, queue, task) {
+  this.addTask(id, priority, queue, task);
+  this.currentTcb.setRunning();
+};
+
+/**
+ * Add the specified task to this scheduler.
+ * @param {int} id the identity of the task
+ * @param {int} priority the task's priority
+ * @param {Packet} queue the queue of work to be processed by the task
+ * @param {Task} task the task to add
+ */
+Scheduler.prototype.addTask = function (id, priority, queue, task) {
+  this.currentTcb = new TaskControlBlock(this.list, id, priority, queue, task);
+  this.list = this.currentTcb;
+  this.blocks[id] = this.currentTcb;
+};
+
+/**
+ * Execute the tasks managed by this scheduler.
+ */
+Scheduler.prototype.schedule = function () {
+  this.currentTcb = this.list;
+  while (this.currentTcb != null) {
+    if (this.currentTcb.isHeldOrSuspended()) {
+      this.currentTcb = this.currentTcb.link;
+    } else {
+      this.currentId = this.currentTcb.id;
+      this.currentTcb = this.currentTcb.run();
+    }
+  }
+};
+
+/**
+ * Release a task that is currently blocked and return the next block to run.
+ * @param {int} id the id of the task to suspend
+ */
+Scheduler.prototype.release = function (id) {
+  var tcb = this.blocks[id];
+  if (tcb == null) return tcb;
+  tcb.markAsNotHeld();
+  if (tcb.priority > this.currentTcb.priority) {
+    return tcb;
+  } else {
+    return this.currentTcb;
+  }
+};
+
+/**
+ * Block the currently executing task and return the next task control block
+ * to run.  The blocked task will not be made runnable until it is explicitly
+ * released, even if new work is added to it.
+ */
+Scheduler.prototype.holdCurrent = function () {
+  this.holdCount++;
+  this.currentTcb.markAsHeld();
+  return this.currentTcb.link;
+};
+
+/**
+ * Suspend the currently executing task and return the next task control block
+ * to run.  If new work is added to the suspended task it will be made runnable.
+ */
+Scheduler.prototype.suspendCurrent = function () {
+  this.currentTcb.markAsSuspended();
+  return this.currentTcb;
+};
+
+/**
+ * Add the specified packet to the end of the worklist used by the task
+ * associated with the packet and make the task runnable if it is currently
+ * suspended.
+ * @param {Packet} packet the packet to add
+ */
+Scheduler.prototype.queue = function (packet) {
+  var t = this.blocks[packet.id];
+  if (t == null) return t;
+  this.queueCount++;
+  packet.link = null;
+  packet.id = this.currentId;
+  return t.checkPriorityAdd(this.currentTcb, packet);
+};
+
+/**
+ * A task control block manages a task and the queue of work packages associated
+ * with it.
+ * @param {TaskControlBlock} link the preceding block in the linked block list
+ * @param {int} id the id of this block
+ * @param {int} priority the priority of this block
+ * @param {Packet} queue the queue of packages to be processed by the task
+ * @param {Task} task the task
+ * @constructor
+ */
+function TaskControlBlock(link, id, priority, queue, task) {
+  this.link = link;
+  this.id = id;
+  this.priority = priority;
+  this.queue = queue;
+  this.task = task;
+  if (queue == null) {
+    this.state = STATE_SUSPENDED;
+  } else {
+    this.state = STATE_SUSPENDED_RUNNABLE;
+  }
+}
+
+/**
+ * The task is running and is currently scheduled.
+ */
+var STATE_RUNNING = 0;
+
+/**
+ * The task has packets left to process.
+ */
+var STATE_RUNNABLE = 1;
+
+/**
+ * The task is not currently running.  The task is not blocked as such and may
+* be started by the scheduler.
+ */
+var STATE_SUSPENDED = 2;
+
+/**
+ * The task is blocked and cannot be run until it is explicitly released.
+ */
+var STATE_HELD = 4;
+
+var STATE_SUSPENDED_RUNNABLE = STATE_SUSPENDED | STATE_RUNNABLE;
+var STATE_NOT_HELD = ~STATE_HELD;
+
+TaskControlBlock.prototype.setRunning = function () {
+  this.state = STATE_RUNNING;
+};
+
+TaskControlBlock.prototype.markAsNotHeld = function () {
+  this.state = this.state & STATE_NOT_HELD;
+};
+
+TaskControlBlock.prototype.markAsHeld = function () {
+  this.state = this.state | STATE_HELD;
+};
+
+TaskControlBlock.prototype.isHeldOrSuspended = function () {
+  return (this.state & STATE_HELD) != 0 || (this.state == STATE_SUSPENDED);
+};
+
+TaskControlBlock.prototype.markAsSuspended = function () {
+  this.state = this.state | STATE_SUSPENDED;
+};
+
+TaskControlBlock.prototype.markAsRunnable = function () {
+  this.state = this.state | STATE_RUNNABLE;
+};
+
+/**
+ * Runs this task, if it is ready to be run, and returns the next task to run.
+ */
+TaskControlBlock.prototype.run = function () {
+  var packet;
+  if (this.state == STATE_SUSPENDED_RUNNABLE) {
+    packet = this.queue;
+    this.queue = packet.link;
+    if (this.queue == null) {
+      this.state = STATE_RUNNING;
+    } else {
+      this.state = STATE_RUNNABLE;
+    }
+  } else {
+    packet = null;
+  }
+  return this.task.run(packet);
+};
+
+/**
+ * Adds a packet to the worklist of this block's task, marks this as runnable if
+ * necessary, and returns the next runnable object to run (the one
+ * with the highest priority).
+ */
+TaskControlBlock.prototype.checkPriorityAdd = function (task, packet) {
+  if (this.queue == null) {
+    this.queue = packet;
+    this.markAsRunnable();
+    if (this.priority > task.priority) return this;
+  } else {
+    this.queue = packet.addTo(this.queue);
+  }
+  return task;
+};
+
+TaskControlBlock.prototype.toString = function () {
+  return "tcb { " + this.task + "@" + this.state + " }";
+};
+
+/**
+ * An idle task doesn't do any work itself but cycles control between the two
+ * device tasks.
+ * @param {Scheduler} scheduler the scheduler that manages this task
+ * @param {int} v1 a seed value that controls how the device tasks are scheduled
+ * @param {int} count the number of times this task should be scheduled
+ * @constructor
+ */
+function IdleTask(scheduler, v1, count) {
+  this.scheduler = scheduler;
+  this.v1 = v1;
+  this.count = count;
+}
+
+IdleTask.prototype.run = function (packet) {
+  this.count--;
+  if (this.count == 0) return this.scheduler.holdCurrent();
+  if ((this.v1 & 1) == 0) {
+    this.v1 = this.v1 >> 1;
+    return this.scheduler.release(ID_DEVICE_A);
+  } else {
+    this.v1 = (this.v1 >> 1) ^ 0xD008;
+    return this.scheduler.release(ID_DEVICE_B);
+  }
+};
+
+IdleTask.prototype.toString = function () {
+  return "IdleTask"
+};
+
+/**
+ * A task that suspends itself after each time it has been run to simulate
+ * waiting for data from an external device.
+ * @param {Scheduler} scheduler the scheduler that manages this task
+ * @constructor
+ */
+function DeviceTask(scheduler) {
+  this.scheduler = scheduler;
+  this.v1 = null;
+}
+
+DeviceTask.prototype.run = function (packet) {
+  if (packet == null) {
+    if (this.v1 == null) return this.scheduler.suspendCurrent();
+    var v = this.v1;
+    this.v1 = null;
+    return this.scheduler.queue(v);
+  } else {
+    this.v1 = packet;
+    return this.scheduler.holdCurrent();
+  }
+};
+
+DeviceTask.prototype.toString = function () {
+  return "DeviceTask";
+};
+
+/**
+ * A task that manipulates work packets.
+ * @param {Scheduler} scheduler the scheduler that manages this task
+ * @param {int} v1 a seed used to specify how work packets are manipulated
+ * @param {int} v2 another seed used to specify how work packets are manipulated
+ * @constructor
+ */
+function WorkerTask(scheduler, v1, v2) {
+  this.scheduler = scheduler;
+  this.v1 = v1;
+  this.v2 = v2;
+}
+
+WorkerTask.prototype.run = function (packet) {
+  if (packet == null) {
+    return this.scheduler.suspendCurrent();
+  } else {
+    if (this.v1 == ID_HANDLER_A) {
+      this.v1 = ID_HANDLER_B;
+    } else {
+      this.v1 = ID_HANDLER_A;
+    }
+    packet.id = this.v1;
+    packet.a1 = 0;
+    for (var i = 0; i < DATA_SIZE; i++) {
+      this.v2++;
+      if (this.v2 > 26) this.v2 = 1;
+      packet.a2[i] = this.v2;
+    }
+    return this.scheduler.queue(packet);
+  }
+};
+
+WorkerTask.prototype.toString = function () {
+  return "WorkerTask";
+};
+
+/**
+ * A task that manipulates work packets and then suspends itself.
+ * @param {Scheduler} scheduler the scheduler that manages this task
+ * @constructor
+ */
+function HandlerTask(scheduler) {
+  this.scheduler = scheduler;
+  this.v1 = null;
+  this.v2 = null;
+}
+
+HandlerTask.prototype.run = function (packet) {
+  if (packet != null) {
+    if (packet.kind == KIND_WORK) {
+      this.v1 = packet.addTo(this.v1);
+    } else {
+      this.v2 = packet.addTo(this.v2);
+    }
+  }
+  if (this.v1 != null) {
+    var count = this.v1.a1;
+    var v;
+    if (count < DATA_SIZE) {
+      if (this.v2 != null) {
+        v = this.v2;
+        this.v2 = this.v2.link;
+        v.a1 = this.v1.a2[count];
+        this.v1.a1 = count + 1;
+        return this.scheduler.queue(v);
+      }
+    } else {
+      v = this.v1;
+      this.v1 = this.v1.link;
+      return this.scheduler.queue(v);
+    }
+  }
+  return this.scheduler.suspendCurrent();
+};
+
+HandlerTask.prototype.toString = function () {
+  return "HandlerTask";
+};
+
+/* --- *
+ * P a c k e t
+ * --- */
+
+var DATA_SIZE = 4;
+
+/**
+ * A simple package of data that is manipulated by the tasks.  The exact layout
+ * of the payload data carried by a packet is not importaint, and neither is the
+ * nature of the work performed on packets by the tasks.
+ *
+ * Besides carrying data, packets form linked lists and are hence used both as
+ * data and worklists.
+ * @param {Packet} link the tail of the linked list of packets
+ * @param {int} id an ID for this packet
+ * @param {int} kind the type of this packet
+ * @constructor
+ */
+function Packet(link, id, kind) {
+  this.link = link;
+  this.id = id;
+  this.kind = kind;
+  this.a1 = 0;
+  this.a2 = new Array(DATA_SIZE);
+}
+
+/**
+ * Add this packet to the end of a worklist, and return the worklist.
+ * @param {Packet} queue the worklist to add this packet to
+ */
+Packet.prototype.addTo = function (queue) {
+  this.link = null;
+  if (queue == null) return this;
+  var peek, next = queue;
+  while ((peek = next.link) != null)
+    next = peek;
+  next.link = this;
+  return queue;
+};
+
+Packet.prototype.toString = function () {
+  return "Packet";
+};
+
+for (var i = 0; i < 20000; ++i)
+  runRichards();

Modified: trunk/Source/_javascript_Core/ChangeLog (236381 => 236382)


--- trunk/Source/_javascript_Core/ChangeLog	2018-09-22 05:26:44 UTC (rev 236381)
+++ trunk/Source/_javascript_Core/ChangeLog	2018-09-22 07:28:39 UTC (rev 236382)
@@ -1,3 +1,28 @@
+2018-09-22  Saam barati  <[email protected]>
+
+        The sampling should not use Strong<CodeBlock> in its machineLocation field
+        https://bugs.webkit.org/show_bug.cgi?id=189319
+
+        Reviewed by Filip Pizlo.
+
+        The sampling profiler has a CLI mode where we gather information about inline
+        call frames. That data structure was using a Strong<CodeBlock>. We were
+        constructing this Strong<CodeBlock> during GC concurrently to processing all
+        the Strong handles. This is a bug since we end up corrupting that data
+        structure. This patch fixes this by just making this data structure use the
+        sampling profiler's mechanism for holding onto and properly visiting heap pointers.
+
+        * inspector/agents/InspectorScriptProfilerAgent.cpp:
+        (Inspector::InspectorScriptProfilerAgent::trackingComplete):
+        * runtime/SamplingProfiler.cpp:
+        (JSC::SamplingProfiler::processUnverifiedStackTraces):
+
+        (JSC::SamplingProfiler::reportTopFunctions):
+        (JSC::SamplingProfiler::reportTopBytecodes):
+        These CLI helpers needed a DeferGC otherwise we may end up deadlocking when we
+        cause a GC to happen while already holding the sampling profiler's
+        lock.
+
 2018-09-21  Yusuke Suzuki  <[email protected]>
 
         [JSC] Enable LLInt ASM interpreter on X64 and ARM64 in non JIT configuration

Modified: trunk/Source/_javascript_Core/inspector/agents/InspectorScriptProfilerAgent.cpp (236381 => 236382)


--- trunk/Source/_javascript_Core/inspector/agents/InspectorScriptProfilerAgent.cpp	2018-09-22 05:26:44 UTC (rev 236381)
+++ trunk/Source/_javascript_Core/inspector/agents/InspectorScriptProfilerAgent.cpp	2018-09-22 07:28:39 UTC (rev 236382)
@@ -207,7 +207,7 @@
     if (m_enabledSamplingProfiler) {
         VM& vm = m_environment.scriptDebugServer().vm();
         JSLockHolder lock(vm);
-        DeferGC deferGC(vm.heap);
+        DeferGC deferGC(vm.heap); // This is required because we will have raw pointers into the heap after we releaseStackTraces().
         SamplingProfiler* samplingProfiler = vm.samplingProfiler();
         RELEASE_ASSERT(samplingProfiler);
 

Modified: trunk/Source/_javascript_Core/runtime/SamplingProfiler.cpp (236381 => 236382)


--- trunk/Source/_javascript_Core/runtime/SamplingProfiler.cpp	2018-09-22 05:26:44 UTC (rev 236381)
+++ trunk/Source/_javascript_Core/runtime/SamplingProfiler.cpp	2018-09-22 07:28:39 UTC (rev 236382)
@@ -567,8 +567,9 @@
                 // output on the command line, but we could extend it to the web
                 // inspector in the future if we find a need for it there.
                 RELEASE_ASSERT(stackTrace.frames.size());
+                m_liveCellPointers.add(machineCodeBlock);
                 for (size_t i = startIndex; i < stackTrace.frames.size() - 1; i++)
-                    stackTrace.frames[i].machineLocation = std::make_pair(machineLocation, Strong<CodeBlock>(m_vm, machineCodeBlock));
+                    stackTrace.frames[i].machineLocation = std::make_pair(machineLocation, machineCodeBlock);
             }
         };
 
@@ -957,6 +958,7 @@
 void SamplingProfiler::reportTopFunctions(PrintStream& out)
 {
     LockHolder locker(m_lock);
+    DeferGCForAWhile deferGC(m_vm.heap);
 
     {
         HeapIterationScope heapIterationScope(m_vm.heap);
@@ -1009,6 +1011,7 @@
 void SamplingProfiler::reportTopBytecodes(PrintStream& out)
 {
     LockHolder locker(m_lock);
+    DeferGCForAWhile deferGC(m_vm.heap);
 
     {
         HeapIterationScope heapIterationScope(m_vm.heap);
@@ -1040,7 +1043,7 @@
 
         StackFrame& frame = stackTrace.frames.first();
         String frameDescription = makeString(frame.displayName(m_vm), descriptionForLocation(frame.semanticLocation));
-        if (std::optional<std::pair<StackFrame::CodeLocation, Strong<CodeBlock>>> machineLocation = frame.machineLocation) {
+        if (std::optional<std::pair<StackFrame::CodeLocation, CodeBlock*>> machineLocation = frame.machineLocation) {
             frameDescription = makeString(frameDescription, " <-- ",
                 machineLocation->second->inferredName().data(), descriptionForLocation(machineLocation->first));
         }

Modified: trunk/Source/_javascript_Core/runtime/SamplingProfiler.h (236381 => 236382)


--- trunk/Source/_javascript_Core/runtime/SamplingProfiler.h	2018-09-22 05:26:44 UTC (rev 236381)
+++ trunk/Source/_javascript_Core/runtime/SamplingProfiler.h	2018-09-22 07:28:39 UTC (rev 236382)
@@ -112,7 +112,7 @@
         };
 
         CodeLocation semanticLocation;
-        std::optional<std::pair<CodeLocation, Strong<CodeBlock>>> machineLocation; // This is non-null if we were inlined. It represents the machine frame we were inlined into.
+        std::optional<std::pair<CodeLocation, CodeBlock*>> machineLocation; // This is non-null if we were inlined. It represents the machine frame we were inlined into.
 
         bool hasExpressionInfo() const { return semanticLocation.hasExpressionInfo(); }
         unsigned lineNumber() const
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