Changeset 241499 in webkit

Timestamp:

Feb 13, 2019 10:43:13 PM (5 years ago)

Author:

rniwa@webkit.org

Message:

Crash in DOMTimer::fired
​https://bugs.webkit.org/show_bug.cgi?id=194638

Reviewed by Brent Fulgham.

Source/WebCore:

This patch continues the saga of hunting down timer related crashes after r239814, r225985, r227934.

The crash was caused by the bug that we don't remove a DOMTimer from NestedTimersMap if a DOMTimer
is created & installed inside another DOMTimer's callback (via execute call in DOMTimer::fired).

Fixed the crash by using a Ref in NestedTimersMap. This will keep the timer alive until we exit
from DOMTimer::fired. Because DOMTimer::fired always calls stopTracking() which clears the map
we would not leak these DOM timers.

We could, alternatively, use WeakPtr in NestedTimersMap but that would unnecessarily increase the
size of DOMTimer for a very marginal benefit of DOMTimer objcets being deleted slightly earlier.
Deleting itself in DOMTimer's destructor involves more logic & house keeping in the timer code,
and is no longer the preferred approach when dealing with these classes of bugs in WebKit.

Test: fast/dom/timer-destruction-during-firing.html

• page/DOMTimer.cpp:

(WebCore::NestedTimersMap::add):
(WebCore::DOMTimer::install):
(WebCore::DOMTimer::fired):

LayoutTests:

Added a regression test. It needs debug assertions without the fix.

• fast/dom/timer-destruction-during-firing-expected.txt: Added.
• fast/dom/timer-destruction-during-firing.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/fast/dom/timer-destruction-during-firing-expected.txt (added)
• LayoutTests/fast/dom/timer-destruction-during-firing.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/page/DOMTimer.cpp (modified) (5 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2019-02-13  Ryosuke Niwa  <rniwa@webkit.org>
+
+        Crash in DOMTimer::fired
+        https://bugs.webkit.org/show_bug.cgi?id=194638
+
+        Reviewed by Brent Fulgham.
+
+        Added a regression test. It needs debug assertions without the fix.
+
+        * fast/dom/timer-destruction-during-firing-expected.txt: Added.
+        * fast/dom/timer-destruction-during-firing.html: Added.
+
 2019-02-13  Nikita Vasilyev  <nvasilyev@apple.com>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2019-02-13  Ryosuke Niwa  <rniwa@webkit.org>
+
+        Crash in DOMTimer::fired
+        https://bugs.webkit.org/show_bug.cgi?id=194638
+
+        Reviewed by Brent Fulgham.
+
+        This patch continues the saga of hunting down timer related crashes after r239814, r225985, r227934.
+
+        The crash was caused by the bug that we don't remove a DOMTimer from NestedTimersMap if a DOMTimer
+        is created & installed inside another DOMTimer's callback (via execute call in DOMTimer::fired).
+
+        Fixed the crash by using a Ref in NestedTimersMap. This will keep the timer alive until we exit
+        from DOMTimer::fired. Because DOMTimer::fired always calls stopTracking() which clears the map
+        we would not leak these DOM timers.
+
+        We could, alternatively, use WeakPtr in NestedTimersMap but that would unnecessarily increase the
+        size of DOMTimer for a very marginal benefit of DOMTimer objcets being deleted slightly earlier.
+        Deleting itself in DOMTimer's destructor involves more logic & house keeping in the timer code,
+        and is no longer the preferred approach when dealing with these classes of bugs in WebKit.
+
+        Test: fast/dom/timer-destruction-during-firing.html
+
+        * page/DOMTimer.cpp:
+        (WebCore::NestedTimersMap::add):
+        (WebCore::DOMTimer::install):
+        (WebCore::DOMTimer::fired):
+
 2019-02-13  Joseph Pecoraro  <pecoraro@apple.com>
 

trunk/Source/WebCore/page/DOMTimer.cpp

@@ -114 +114 @@
 
 struct NestedTimersMap {
-    typedef HashMap<int, DOMTimer*>::const_iterator const_iterator;
+    typedef HashMap<int, Ref<DOMTimer>>::const_iterator const_iterator;
 
     static NestedTimersMap* instanceForContext(ScriptExecutionContext& context)
@@ -140 +140 @@
     }
 
-    void add(int timeoutId, DOMTimer* timer)
+    void add(int timeoutId, Ref<DOMTimer>&& timer)
     {
         if (isTrackingNestedTimers)
-            nestedTimers.add(timeoutId, timer);
+            nestedTimers.add(timeoutId, WTFMove(timer));
     }
 
@@ -163 +163 @@
 
     static bool isTrackingNestedTimers;
-    HashMap<int /* timeoutId */, DOMTimer*> nestedTimers;
+    HashMap<int /* timeoutId */, Ref<DOMTimer>> nestedTimers;
 };
 
@@ -236 +236 @@
     // Keep track of nested timer installs.
     if (NestedTimersMap* nestedTimers = NestedTimersMap::instanceForContext(context))
-        nestedTimers->add(timer->m_timeoutId, timer);
+        nestedTimers->add(timer->m_timeoutId, *timer);
 
     return timer->m_timeoutId;
@@ -391 +391 @@
     // Check if we should throttle nested single-shot timers.
     if (nestedTimers) {
-        for (auto& keyValue : *nestedTimers) {
-            auto* timer = keyValue.value;
+        for (auto& idAndTimer : *nestedTimers) {
+            auto& timer = idAndTimer.value;
             if (timer->isActive() && !timer->repeatInterval())
                 timer->updateThrottlingStateIfNecessary(fireState);