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Fix the "PersistentValueMap" memory leak reported here:

Browse Source 
http://build.chromium.org/p/client.v8/builders/V8%20Linux64%20ASAN

The bug:
The code assumed that a weak Persistent whose weak callback is being
called would still be weak. That isn't true since the persistent is
un-weakened by the garbage collector before calling the weak callback. [1]

Specifically, PersistentValueMap would funnel all 'remove' actions
through its Release method, which uses PersistentBase::ClearWeak to
obtain the callback data. [2] For 'removes' caused by the weak callback,
ClearWeak always returns a NULL-pointer since by that time the weak
persistent was already un-weakend. The result was a memory leak in
the test, since the code to delete the weak callback data would
delete NULL.

The fix:
I explicity call Traits::DisposeCallbackData from the weak callback
with the data obtained from the v8::WeakCallbackData. To avoid invalid
calls to DisposeCallbackData, I also check whether this instance is
(still) weak before calling it. (That check could easily be elided
if it's expensive, for the price of having two 'remove' code paths.)

Severety:
Probably low. At least in Chromium, noone uses the API in a way to
trigger this; only the test does.

[1] https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/global-handles.cc&q=global-handles.cc&sq=package:chromium&type=cs&l=231
[2] https://code.google.com/p/chromium/codesearch#chromium/src/v8/include/v8-util.h&sq=package:chromium&l=332-345

R=dcarney@chromium.org, dcarney

BUG=

Review URL: https://codereview.chromium.org/297193004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21514 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
vogelheim@chromium.org 2014-05-27 09:31:06 +00:00
parent 0fde744d00
commit 06086a90e0
1 changed files with 2 additions and 1 deletions
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3
include/v8-util.h
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@ -300,6 +300,7 @@ class PersistentValueMap {
K key = Traits::KeyFromWeakCallbackData(data);
Traits::Dispose(data.GetIsolate(),
persistentValueMap->Remove(key).Pass(), key);
Traits::DisposeCallbackData(data.GetParameter());
}
}
@ -337,7 +338,7 @@ class PersistentValueMap {
static UniquePersistent<V> Release(PersistentContainerValue v) {
UniquePersistent<V> p;
p.val_ = FromVal(v);
if (Traits::kCallbackType != kNotWeak && !p.IsEmpty()) {
if (Traits::kCallbackType != kNotWeak && p.IsWeak()) {
Traits::DisposeCallbackData(
p.template ClearWeak<typename Traits::WeakCallbackDataType>());
}