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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/193690">193690</a></dd>
<dt>Author</dt> <dd>ddkilzer@apple.com</dd>
<dt>Date</dt> <dd>2015-12-07 21:05:32 -0800 (Mon, 07 Dec 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/193635">r193635</a>. rdar://problem/23785592</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#branchessafari601146branchSourceWebCoreChangeLog">branches/safari-601.1.46-branch/Source/WebCore/ChangeLog</a></li>
<li><a href="#branchessafari601146branchSourceWebCoreloadercacheMemoryCachecpp">branches/safari-601.1.46-branch/Source/WebCore/loader/cache/MemoryCache.cpp</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="branchessafari601146branchSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: branches/safari-601.1.46-branch/Source/WebCore/ChangeLog (193689 => 193690)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-601.1.46-branch/Source/WebCore/ChangeLog        2015-12-08 04:59:08 UTC (rev 193689)
+++ branches/safari-601.1.46-branch/Source/WebCore/ChangeLog        2015-12-08 05:05:32 UTC (rev 193690)
</span><span class="lines">@@ -1,3 +1,42 @@
</span><ins>+2015-12-07 David Kilzer <ddkilzer@apple.com>
+
+ Merge r193635. rdar://problem/23785592
+
+ 2015-12-07 Chris Dumez <cdumez@apple.com>
+
+ Crash in MemoryCache::pruneDeadResourcesToSize()
+ https://bugs.webkit.org/show_bug.cgi?id=151833
+ <rdar://problem/22392235>
+
+ Reviewed by David Kilzer.
+
+ MemoryCache::pruneDeadResourcesToSize() is iterating over m_allResources
+ (which is a vector of LRUList). It first destroys decoded data for each
+ resource in the LRUList. Then, if it does not suffice to reach the
+ target size, and starts actually removing resources from the cache.
+
+ The issue is that this code alters m_allResources (and its LRULists) as
+ it is iterating over it. We tried to deal with this in various ways:
+ 1. Increment the iterator before removing the resource pointed by the
+ iterator.
+ 2. Protect the next resource in the LRUList and abort early if it is no
+ longer in the cache.
+
+ This adds code complexity and apparently does not correctly handle all
+ the edge cases as we still see crashes in this code. In particular, I
+ suspect that 2. may not be sufficient if it is possible for the next
+ resource to be moved to another LRUList (in which case, next->inCache()
+ would still return true but the iterator would however become invalid).
+
+ To make the code simpler and more robust, this patch copies the LRUList
+ (and refs the CachedResources) before iterating over it. This is a lot
+ safer and should hopefully fix the crashes we see in this function.
+
+ No new tests, no reproduction case.
+
+ * loader/cache/MemoryCache.cpp:
+ (WebCore::MemoryCache::pruneDeadResourcesToSize):
+
</ins><span class="cx"> 2015-12-06 Babak Shafiei <bshafiei@apple.com>
</span><span class="cx">
</span><span class="cx"> Merge r193599.
</span></span></pre></div>
<a id="branchessafari601146branchSourceWebCoreloadercacheMemoryCachecpp"></a>
<div class="modfile"><h4>Modified: branches/safari-601.1.46-branch/Source/WebCore/loader/cache/MemoryCache.cpp (193689 => 193690)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-601.1.46-branch/Source/WebCore/loader/cache/MemoryCache.cpp        2015-12-08 04:59:08 UTC (rev 193689)
+++ branches/safari-601.1.46-branch/Source/WebCore/loader/cache/MemoryCache.cpp        2015-12-08 05:05:32 UTC (rev 193690)
</span><span class="lines">@@ -348,55 +348,39 @@
</span><span class="cx">
</span><span class="cx"> bool canShrinkLRULists = true;
</span><span class="cx"> for (int i = m_allResources.size() - 1; i >= 0; i--) {
</span><del>- LRUList& list = *m_allResources[i];
</del><ins>+ // Make a copy of the LRUList first (and ref the resources) as calling
+ // destroyDecodedData() can alter the LRUList.
+ Vector<CachedResourceHandle<CachedResource>> lruList;
+ copyToVector(*m_allResources[i], lruList);
</ins><span class="cx">
</span><span class="cx"> // First flush all the decoded data in this queue.
</span><span class="cx"> // Remove from the head, since this is the least frequently accessed of the objects.
</span><del>- auto it = list.begin();
- while (it != list.end()) {
- CachedResource& current = **it;
</del><ins>+ for (auto& resource : lruList) {
+ if (!resource->inCache())
+ continue;
</ins><span class="cx">
</span><del>- // Increment the iterator now as the call to destroyDecodedData() below may
- // invalidate the current iterator.
- ++it;
-
- // Protect 'next' so it can't get deleted during destroyDecodedData().
- CachedResourceHandle<CachedResource> next = it != list.end() ? *it : nullptr;
- ASSERT(!next || next->inCache());
- if (!current.hasClients() && !current.isPreloaded() && current.isLoaded()) {
</del><ins>+ if (!resource->hasClients() && !resource->isPreloaded() && resource->isLoaded()) {
</ins><span class="cx"> // Destroy our decoded data. This will remove us from
</span><span class="cx"> // m_liveDecodedResources, and possibly move us to a different
</span><span class="cx"> // LRU list in m_allResources.
</span><del>- current.destroyDecodedData();
</del><ins>+ resource->destroyDecodedData();
</ins><span class="cx">
</span><span class="cx"> if (targetSize && m_deadSize <= targetSize)
</span><span class="cx"> return;
</span><span class="cx"> }
</span><del>- // Decoded data may reference other resources. Stop iterating if 'next' somehow got
- // kicked out of cache during destroyDecodedData().
- if (next && !next->inCache())
- break;
</del><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> // Now evict objects from this list.
</span><span class="cx"> // Remove from the head, since this is the least frequently accessed of the objects.
</span><del>- it = list.begin();
- while (it != list.end()) {
- CachedResource& current = **it;
</del><ins>+ for (auto& resource : lruList) {
+ if (!resource->inCache())
+ continue;
</ins><span class="cx">
</span><del>- // Increment the iterator now as the call to remove() below will
- // invalidate the current iterator.
- ++it;
-
- CachedResourceHandle<CachedResource> next = it != list.end() ? *it : nullptr;
- ASSERT(!next || next->inCache());
- if (!current.hasClients() && !current.isPreloaded() && !current.isCacheValidator()) {
- remove(current);
</del><ins>+ if (!resource->hasClients() && !resource->isPreloaded() && !resource->isCacheValidator()) {
+ remove(*resource);
</ins><span class="cx"> if (targetSize && m_deadSize <= targetSize)
</span><span class="cx"> return;
</span><span class="cx"> }
</span><del>- if (next && !next->inCache())
- break;
</del><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> // Shrink the vector back down so we don't waste time inspecting
</span></span></pre>
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