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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/167692">167692</a></dd>
<dt>Author</dt> <dd>mark.lam@apple.com</dd>
<dt>Date</dt> <dd>2014-04-22 17:36:49 -0700 (Tue, 22 Apr 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>DFG::Worklist should acquire the m_lock before iterating DFG plans.
<https://webkit.org/b/132032>
Reviewed by Filip Pizlo.
Currently, there's a rightToRun mechanism that ensures that no compilation
threads are running when the GC is iterating through the DFG worklists.
However, this does not prevent a Worker thread from doing a DFG compilation
and modifying the plans in the worklists thereby invalidating the plan
iterator that the GC is using. This patch fixes the issue by acquiring
the worklist m_lock before iterating the worklist plans.
This issue was uncovered by running the fast/workers layout tests with
COLLECT_ON_EVERY_ALLOCATION enabled.
* dfg/DFGWorklist.cpp:
(JSC::DFG::Worklist::isActiveForVM):
(JSC::DFG::Worklist::visitChildren):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGWorklistcpp">trunk/Source/JavaScriptCore/dfg/DFGWorklist.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (167691 => 167692)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-04-22 23:54:49 UTC (rev 167691)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-04-23 00:36:49 UTC (rev 167692)
</span><span class="lines">@@ -1,3 +1,24 @@
</span><ins>+2014-04-22 Mark Lam <mark.lam@apple.com>
+
+ DFG::Worklist should acquire the m_lock before iterating DFG plans.
+ <https://webkit.org/b/132032>
+
+ Reviewed by Filip Pizlo.
+
+ Currently, there's a rightToRun mechanism that ensures that no compilation
+ threads are running when the GC is iterating through the DFG worklists.
+ However, this does not prevent a Worker thread from doing a DFG compilation
+ and modifying the plans in the worklists thereby invalidating the plan
+ iterator that the GC is using. This patch fixes the issue by acquiring
+ the worklist m_lock before iterating the worklist plans.
+
+ This issue was uncovered by running the fast/workers layout tests with
+ COLLECT_ON_EVERY_ALLOCATION enabled.
+
+ * dfg/DFGWorklist.cpp:
+ (JSC::DFG::Worklist::isActiveForVM):
+ (JSC::DFG::Worklist::visitChildren):
+
</ins><span class="cx"> 2014-04-22 Brent Fulgham <bfulgham@apple.com>
</span><span class="cx">
</span><span class="cx"> [Win] Support Python 2.7 in Cygwin
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGWorklistcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGWorklist.cpp (167691 => 167692)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGWorklist.cpp 2014-04-22 23:54:49 UTC (rev 167691)
+++ trunk/Source/JavaScriptCore/dfg/DFGWorklist.cpp 2014-04-23 00:36:49 UTC (rev 167692)
</span><span class="lines">@@ -76,6 +76,7 @@
</span><span class="cx">
</span><span class="cx"> bool Worklist::isActiveForVM(VM& vm) const
</span><span class="cx"> {
</span><ins>+ MutexLocker locker(m_lock);
</ins><span class="cx"> PlanMap::const_iterator end = m_plans.end();
</span><span class="cx"> for (PlanMap::const_iterator iter = m_plans.begin(); iter != end; ++iter) {
</span><span class="cx"> if (&iter->value->vm == &vm)
</span><span class="lines">@@ -222,14 +223,21 @@
</span><span class="cx"> void Worklist::visitChildren(SlotVisitor& visitor, CodeBlockSet& codeBlocks)
</span><span class="cx"> {
</span><span class="cx"> VM* vm = visitor.heap()->vm();
</span><del>- for (PlanMap::iterator iter = m_plans.begin(); iter != m_plans.end(); ++iter) {
- Plan* plan = iter->value.get();
- if (&plan->vm != vm)
- continue;
- iter->key.visitChildren(codeBlocks);
- iter->value->visitChildren(visitor, codeBlocks);
</del><ins>+ {
+ MutexLocker locker(m_lock);
+ for (PlanMap::iterator iter = m_plans.begin(); iter != m_plans.end(); ++iter) {
+ Plan* plan = iter->value.get();
+ if (&plan->vm != vm)
+ continue;
+ iter->key.visitChildren(codeBlocks);
+ iter->value->visitChildren(visitor, codeBlocks);
+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><ins>+ // This loop doesn't need further locking because:
+ // (1) no new threads can be added to m_threads. Hence, it is immutable and needs no locks.
+ // (2) ThreadData::m_safepoint is protected by that thread's m_rightToRun which we must be
+ // holding here because of a prior call to suspendAllThreads().
</ins><span class="cx"> for (unsigned i = m_threads.size(); i--;) {
</span><span class="cx"> ThreadData* data = m_threads[i].get();
</span><span class="cx"> Safepoint* safepoint = data->m_safepoint;
</span></span></pre>
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