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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/164687">164687</a></dd>
<dt>Author</dt> <dd>mark.lam@apple.com</dd>
<dt>Date</dt> <dd>2014-02-25 18:12:57 -0800 (Tue, 25 Feb 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Web Inspector: CRASH when evaluating in console of JSContext RWI with disabled breakpoints.
<https://webkit.org/b/128766>
Reviewed by Geoffrey Garen.
Make the JSLock::grabAllLocks() work the same way as for the C loop LLINT.
The reasoning is that we don't know of any clients that need unordered
re-entry into the VM from different threads. So, we're enforcing ordered
re-entry i.e. we must re-grab locks in the reverse order of dropping locks.
The crash in this bug happened because we were allowing unordered re-entry,
and the following type of scenario occurred:
1. Thread T1 locks the VM, and enters the VM to execute some JS code.
2. On entry, T1 detects that VM::m_entryScope is null i.e. this is the
first time it entered the VM.
T1 sets VM::m_entryScope to T1's entryScope.
3. T1 drops all locks.
4. Thread T2 locks the VM, and enters the VM to execute some JS code.
On entry, T2 sees that VM::m_entryScope is NOT null, and therefore
does not set the entryScope.
5. T2 drops all locks.
6. T1 re-grabs locks.
7. T1 returns all the way out of JS code. On exit from the outer most
JS function, T1 clears VM::m_entryScope (because T1 was the one who
set it).
8. T1 unlocks the VM.
9. T2 re-grabs locks.
10. T2 proceeds to execute some code and expects VM::m_entryScope to be
NOT null, but it turns out to be null. Assertion failures and
crashes ensue.
With ordered re-entry, at step 6, T1 will loop and yield until T2 exits
the VM. Hence, the issue will no longer manifest.
* runtime/JSLock.cpp:
(JSC::JSLock::dropAllLocks):
(JSC::JSLock::grabAllLocks):
* runtime/JSLock.h:
(JSC::JSLock::DropAllLocks::dropDepth):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSLockcpp">trunk/Source/JavaScriptCore/runtime/JSLock.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSLockh">trunk/Source/JavaScriptCore/runtime/JSLock.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (164686 => 164687)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2014-02-26 01:45:52 UTC (rev 164686)
+++ trunk/Source/JavaScriptCore/ChangeLog 2014-02-26 02:12:57 UTC (rev 164687)
</span><span class="lines">@@ -1,5 +1,51 @@
</span><span class="cx"> 2014-02-25 Mark Lam <mark.lam@apple.com>
</span><span class="cx">
</span><ins>+ Web Inspector: CRASH when evaluating in console of JSContext RWI with disabled breakpoints.
+ <https://webkit.org/b/128766>
+
+ Reviewed by Geoffrey Garen.
+
+ Make the JSLock::grabAllLocks() work the same way as for the C loop LLINT.
+ The reasoning is that we don't know of any clients that need unordered
+ re-entry into the VM from different threads. So, we're enforcing ordered
+ re-entry i.e. we must re-grab locks in the reverse order of dropping locks.
+
+ The crash in this bug happened because we were allowing unordered re-entry,
+ and the following type of scenario occurred:
+
+ 1. Thread T1 locks the VM, and enters the VM to execute some JS code.
+ 2. On entry, T1 detects that VM::m_entryScope is null i.e. this is the
+ first time it entered the VM.
+ T1 sets VM::m_entryScope to T1's entryScope.
+ 3. T1 drops all locks.
+
+ 4. Thread T2 locks the VM, and enters the VM to execute some JS code.
+ On entry, T2 sees that VM::m_entryScope is NOT null, and therefore
+ does not set the entryScope.
+ 5. T2 drops all locks.
+
+ 6. T1 re-grabs locks.
+ 7. T1 returns all the way out of JS code. On exit from the outer most
+ JS function, T1 clears VM::m_entryScope (because T1 was the one who
+ set it).
+ 8. T1 unlocks the VM.
+
+ 9. T2 re-grabs locks.
+ 10. T2 proceeds to execute some code and expects VM::m_entryScope to be
+ NOT null, but it turns out to be null. Assertion failures and
+ crashes ensue.
+
+ With ordered re-entry, at step 6, T1 will loop and yield until T2 exits
+ the VM. Hence, the issue will no longer manifest.
+
+ * runtime/JSLock.cpp:
+ (JSC::JSLock::dropAllLocks):
+ (JSC::JSLock::grabAllLocks):
+ * runtime/JSLock.h:
+ (JSC::JSLock::DropAllLocks::dropDepth):
+
+2014-02-25 Mark Lam <mark.lam@apple.com>
+
</ins><span class="cx"> Need to initialize VM stack data even when the VM is on an exclusive thread.
</span><span class="cx"> <https://webkit.org/b/129265>
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSLockcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSLock.cpp (164686 => 164687)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSLock.cpp 2014-02-26 01:45:52 UTC (rev 164686)
+++ trunk/Source/JavaScriptCore/runtime/JSLock.cpp 2014-02-26 02:12:57 UTC (rev 164687)
</span><span class="lines">@@ -26,9 +26,7 @@
</span><span class="cx"> #include "JSGlobalObject.h"
</span><span class="cx"> #include "JSObject.h"
</span><span class="cx"> #include "JSCInlines.h"
</span><del>-#if ENABLE(LLINT_C_LOOP)
</del><span class="cx"> #include <thread>
</span><del>-#endif
</del><span class="cx">
</span><span class="cx"> namespace JSC {
</span><span class="cx">
</span><span class="lines">@@ -192,10 +190,7 @@
</span><span class="cx">
</span><span class="cx"> ++m_lockDropDepth;
</span><span class="cx">
</span><del>- UNUSED_PARAM(dropper);
-#if ENABLE(LLINT_C_LOOP)
</del><span class="cx"> dropper->setDropDepth(m_lockDropDepth);
</span><del>-#endif
</del><span class="cx">
</span><span class="cx"> WTFThreadData& threadData = wtfThreadData();
</span><span class="cx"> threadData.setSavedStackPointerAtVMEntry(m_vm->stackPointerAtVMEntry());
</span><span class="lines">@@ -218,14 +213,11 @@
</span><span class="cx"> ASSERT(!currentThreadIsHoldingLock());
</span><span class="cx"> lock(droppedLockCount);
</span><span class="cx">
</span><del>- UNUSED_PARAM(dropper);
-#if ENABLE(LLINT_C_LOOP)
</del><span class="cx"> while (dropper->dropDepth() != m_lockDropDepth) {
</span><span class="cx"> unlock(droppedLockCount);
</span><span class="cx"> std::this_thread::yield();
</span><span class="cx"> lock(droppedLockCount);
</span><span class="cx"> }
</span><del>-#endif
</del><span class="cx">
</span><span class="cx"> --m_lockDropDepth;
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSLockh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSLock.h (164686 => 164687)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSLock.h 2014-02-26 01:45:52 UTC (rev 164686)
+++ trunk/Source/JavaScriptCore/runtime/JSLock.h 2014-02-26 02:12:57 UTC (rev 164687)
</span><span class="lines">@@ -112,17 +112,13 @@
</span><span class="cx"> JS_EXPORT_PRIVATE DropAllLocks(VM*);
</span><span class="cx"> JS_EXPORT_PRIVATE ~DropAllLocks();
</span><span class="cx">
</span><del>-#if ENABLE(LLINT_C_LOOP)
</del><span class="cx"> void setDropDepth(unsigned depth) { m_dropDepth = depth; }
</span><span class="cx"> unsigned dropDepth() const { return m_dropDepth; }
</span><del>-#endif
</del><span class="cx">
</span><span class="cx"> private:
</span><span class="cx"> intptr_t m_droppedLockCount;
</span><span class="cx"> RefPtr<VM> m_vm;
</span><del>-#if ENABLE(LLINT_C_LOOP)
</del><span class="cx"> unsigned m_dropDepth;
</span><del>-#endif
</del><span class="cx"> };
</span><span class="cx">
</span><span class="cx"> private:
</span></span></pre>
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