Bug 104922 – [WK2] Frequent NetworkProcess crashes due to null connection when closing tabs

• Component: WebKit2
• Status: RESOLVED FIXED

[Alexey Proskuryakov]

When a tab is closed, WebProcess goes away, but NetworkProcess will still sometimes attempt to send messages to it if there were outstanding loads.

NetworkResourceLoader and NetworkConnectionToWebProcess both have m_connection that is zeroed on on connection close, and that causes null pointer crashes in IPC machinery.

This is easy to reproduce on sites that use long-standing connections, like gmail.

<rdar://problem/12870065>

[Alexey Proskuryakov]

Created attachment 179283 [details]
proposed patch

[Oliver Hunt]

Comment on attachment 179283 [details]
proposed patch

View in context: https://bugs.webkit.org/attachment.cgi?id=179283&action=review

> Source/WebKit2/NetworkProcess/NetworkResourceLoader.cpp:-147
> -    m_connection->unregisterObserver(this);

Why arbitrarily delta this and not have if (RefPtr<blah> connection = m_connection) connection->unregisterObserver(this) ?

> Source/WebKit2/NetworkProcess/NetworkResourceLoader.cpp:-148
> -    m_connection = 0;

If connection is null this doesn't hurt, does it hurt to explicitly clear m_connection if it is non-null?

[Alexey Proskuryakov]

Comment on attachment 179283 [details]
proposed patch

View in context: https://bugs.webkit.org/attachment.cgi?id=179283&action=review

>> Source/WebKit2/NetworkProcess/NetworkResourceLoader.cpp:-147
>> -    m_connection->unregisterObserver(this);
> 
> Why arbitrarily delta this and not have if (RefPtr<blah> connection = m_connection) connection->unregisterObserver(this) ?

There is another unregisterObserver call in destructor, there is no reason to do this twice.

>> Source/WebKit2/NetworkProcess/NetworkResourceLoader.cpp:-148
>> -    m_connection = 0;
> 
> If connection is null this doesn't hurt, does it hurt to explicitly clear m_connection if it is non-null?

I'm not sure if I understand the question.

m_connection being null is why this crash happens, so it definitely hurts to clear it.

[Alexey Proskuryakov]

Committed <http://trac.webkit.org/changeset/137610>.