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<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/179648">179648</a></dd>
<dt>Author</dt> <dd>mark.lam@apple.com</dd>
<dt>Date</dt> <dd>2015-02-04 16:32:47 -0800 (Wed, 04 Feb 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre><a href="http://trac.webkit.org/projects/webkit/changeset/179576">r179576</a> introduce a deadlock potential during GC thread suspension.
<https://webkit.org/b/141268>
Reviewed by Michael Saboff.
http://trac.webkit.org/<a href="http://trac.webkit.org/projects/webkit/changeset/179576">r179576</a> introduced a potential for deadlocking.
In the GC thread suspension loop, we currently delete
MachineThreads::Thread that we detect to be invalid. This is unsafe
because we may have already suspended some threads, and one of those
suspended threads may still be holding the C heap lock which we need
for deleting the invalid thread.
The fix is to put the invalid threads in a separate toBeDeleted list,
and delete them only after GC has resumed all threads.
* heap/MachineStackMarker.cpp:
(JSC::MachineThreads::removeCurrentThread):
- Undo refactoring removeThreadWithLockAlreadyAcquired() out of
removeCurrentThread() since it is no longer needed.
(JSC::MachineThreads::tryCopyOtherThreadStacks):
- Put invalid Threads on a threadsToBeDeleted list, and delete those
Threads only after all threads have been resumed.
(JSC::MachineThreads::removeThreadWithLockAlreadyAcquired): Deleted.
* heap/MachineStackMarker.h:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMachineStackMarkercpp">trunk/Source/JavaScriptCore/heap/MachineStackMarker.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreheapMachineStackMarkerh">trunk/Source/JavaScriptCore/heap/MachineStackMarker.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (179647 => 179648)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2015-02-05 00:32:27 UTC (rev 179647)
+++ trunk/Source/JavaScriptCore/ChangeLog 2015-02-05 00:32:47 UTC (rev 179648)
</span><span class="lines">@@ -1,3 +1,32 @@
</span><ins>+2015-02-04 Mark Lam <mark.lam@apple.com>
+
+ r179576 introduce a deadlock potential during GC thread suspension.
+ <https://webkit.org/b/141268>
+
+ Reviewed by Michael Saboff.
+
+ http://trac.webkit.org/r179576 introduced a potential for deadlocking.
+ In the GC thread suspension loop, we currently delete
+ MachineThreads::Thread that we detect to be invalid. This is unsafe
+ because we may have already suspended some threads, and one of those
+ suspended threads may still be holding the C heap lock which we need
+ for deleting the invalid thread.
+
+ The fix is to put the invalid threads in a separate toBeDeleted list,
+ and delete them only after GC has resumed all threads.
+
+ * heap/MachineStackMarker.cpp:
+ (JSC::MachineThreads::removeCurrentThread):
+ - Undo refactoring removeThreadWithLockAlreadyAcquired() out of
+ removeCurrentThread() since it is no longer needed.
+
+ (JSC::MachineThreads::tryCopyOtherThreadStacks):
+ - Put invalid Threads on a threadsToBeDeleted list, and delete those
+ Threads only after all threads have been resumed.
+
+ (JSC::MachineThreads::removeThreadWithLockAlreadyAcquired): Deleted.
+ * heap/MachineStackMarker.h:
+
</ins><span class="cx"> 2015-02-04 Joseph Pecoraro <pecoraro@apple.com>
</span><span class="cx">
</span><span class="cx"> Web Inspector: Clean up Object Property Descriptor Collection
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMachineStackMarkercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MachineStackMarker.cpp (179647 => 179648)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MachineStackMarker.cpp 2015-02-05 00:32:27 UTC (rev 179647)
+++ trunk/Source/JavaScriptCore/heap/MachineStackMarker.cpp 2015-02-05 00:32:47 UTC (rev 179648)
</span><span class="lines">@@ -183,10 +183,12 @@
</span><span class="cx"> static_cast<MachineThreads*>(p)->removeCurrentThread();
</span><span class="cx"> }
</span><span class="cx">
</span><del>-template<typename PlatformThread>
-void MachineThreads::removeThreadWithLockAlreadyAcquired(PlatformThread threadToRemove)
</del><ins>+void MachineThreads::removeCurrentThread()
</ins><span class="cx"> {
</span><del>- if (equalThread(threadToRemove, m_registeredThreads->platformThread)) {
</del><ins>+ PlatformThread currentPlatformThread = getCurrentPlatformThread();
+
+ MutexLocker lock(m_registeredThreadsMutex);
+ if (equalThread(currentPlatformThread, m_registeredThreads->platformThread)) {
</ins><span class="cx"> Thread* t = m_registeredThreads;
</span><span class="cx"> m_registeredThreads = m_registeredThreads->next;
</span><span class="cx"> delete t;
</span><span class="lines">@@ -194,7 +196,7 @@
</span><span class="cx"> Thread* last = m_registeredThreads;
</span><span class="cx"> Thread* t;
</span><span class="cx"> for (t = m_registeredThreads->next; t; t = t->next) {
</span><del>- if (equalThread(t->platformThread, threadToRemove)) {
</del><ins>+ if (equalThread(t->platformThread, currentPlatformThread)) {
</ins><span class="cx"> last->next = t->next;
</span><span class="cx"> break;
</span><span class="cx"> }
</span><span class="lines">@@ -205,14 +207,6 @@
</span><span class="cx"> }
</span><span class="cx"> }
</span><span class="cx">
</span><del>-void MachineThreads::removeCurrentThread()
-{
- PlatformThread currentPlatformThread = getCurrentPlatformThread();
-
- MutexLocker lock(m_registeredThreadsMutex);
- removeThreadWithLockAlreadyAcquired(currentPlatformThread);
-}
-
</del><span class="cx"> void MachineThreads::gatherFromCurrentThread(ConservativeRoots& conservativeRoots, JITStubRoutineSet& jitStubRoutines, CodeBlockSet& codeBlocks, void* stackCurrent, RegisterState& registers)
</span><span class="cx"> {
</span><span class="cx"> void* registersBegin = &registers;
</span><span class="lines">@@ -456,7 +450,9 @@
</span><span class="cx"> PlatformThread currentPlatformThread = getCurrentPlatformThread();
</span><span class="cx"> int numberOfThreads = 0; // Using 0 to denote that we haven't counted the number of threads yet.
</span><span class="cx"> int index = 1;
</span><ins>+ Thread* threadsToBeDeleted = nullptr;
</ins><span class="cx">
</span><ins>+ Thread* previousThread = nullptr;
</ins><span class="cx"> for (Thread* thread = m_registeredThreads; thread; index++) {
</span><span class="cx"> if (!equalThread(thread->platformThread, currentPlatformThread)) {
</span><span class="cx"> bool success = suspendThread(thread->platformThread);
</span><span class="lines">@@ -474,9 +470,20 @@
</span><span class="cx"> WTFReportError(__FILE__, __LINE__, WTF_PRETTY_FUNCTION,
</span><span class="cx"> "JavaScript garbage collection encountered an invalid thread (err 0x%x): Thread [%d/%d: %p] platformThread %p.",
</span><span class="cx"> error, index, numberOfThreads, thread, reinterpret_cast<void*>(thread->platformThread));
</span><del>-
</del><ins>+
+ // Put the invalid thread on the threadsToBeDeleted list.
+ // We can't just delete it here because we have suspended other
+ // threads, and they may still be holding the C heap lock which
+ // we need for deleting the invalid thread. Hence, we need to
+ // defer the deletion till after we have resumed all threads.
</ins><span class="cx"> Thread* nextThread = thread->next;
</span><del>- removeThreadWithLockAlreadyAcquired(thread->platformThread);
</del><ins>+ thread->next = threadsToBeDeleted;
+ threadsToBeDeleted = thread;
+
+ if (previousThread)
+ previousThread->next = nextThread;
+ else
+ m_registeredThreads = nextThread;
</ins><span class="cx"> thread = nextThread;
</span><span class="cx"> continue;
</span><span class="cx"> }
</span><span class="lines">@@ -485,6 +492,7 @@
</span><span class="cx"> ASSERT_UNUSED(success, success);
</span><span class="cx"> #endif
</span><span class="cx"> }
</span><ins>+ previousThread = thread;
</ins><span class="cx"> thread = thread->next;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -498,6 +506,12 @@
</span><span class="cx"> resumeThread(thread->platformThread);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ for (Thread* thread = threadsToBeDeleted; thread; ) {
+ Thread* nextThread = thread->next;
+ delete thread;
+ thread = nextThread;
+ }
+
</ins><span class="cx"> return *size <= capacity;
</span><span class="cx"> }
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreheapMachineStackMarkerh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/heap/MachineStackMarker.h (179647 => 179648)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/heap/MachineStackMarker.h 2015-02-05 00:32:27 UTC (rev 179647)
+++ trunk/Source/JavaScriptCore/heap/MachineStackMarker.h 2015-02-05 00:32:47 UTC (rev 179648)
</span><span class="lines">@@ -57,9 +57,6 @@
</span><span class="cx"> static void removeThread(void*);
</span><span class="cx"> void removeCurrentThread();
</span><span class="cx">
</span><del>- template<typename PlatformThread>
- void removeThreadWithLockAlreadyAcquired(PlatformThread);
-
</del><span class="cx"> Mutex m_registeredThreadsMutex;
</span><span class="cx"> Thread* m_registeredThreads;
</span><span class="cx"> WTF::ThreadSpecificKey m_threadSpecific;
</span></span></pre>
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