Bug 173473 – Cleanup IconLoader stuff when a DocumentLoader detaches from its frame

• Component: WebCore Misc.
• Status: RESOLVED FIXED

[Brady Eidson]

Null deref crash in DocumentLoader::finishedLoadingIcon

Specifically, deref'ing a null frame.

0   com.apple.WebCore             	0x000000010faa91fd WebCore::DocumentLoader::finishedLoadingIcon(WebCore::IconLoader&, WebCore::SharedBuffer*) + 29
1   com.apple.WebCore             	0x000000010f8dc3fd WebCore::CachedResource::didAddClient(WebCore::CachedResourceClient&) + 205
2   com.apple.WebCore             	0x000000010f8d9ad6 WebCore::CachedRawResource::didAddClient(WebCore::CachedResourceClient&) + 758
3   com.apple.WebCore             	0x000000010f60f870 WebCore::ThreadTimers::sharedTimerFiredInternal() + 176
4   com.apple.WebCore             	0x000000010f60f7af WebCore::timerFired(__CFRunLoopTimer*, void*) + 31

I have not been able to reproduce.

I've been able to figure out a sequence of events to reproduce this:

0 - Be using an embedding app that uses the icon loading delegate API.
1 - Visit a website that references a site icon.
2 - The embedding app says "yes, load it".
3 - The icon is loaded as a sub resource, and that includes putting it in the memory cache.
4 - Navigate to another page within the same website that will load the same icon.
5 - Embedding app says "yes, load it"
6 - DocumentLoader - still attached to a frame - creates an IconLoader for the icon
7 - The IconLoader goes through the memory cache to get at a CachedResource for the icon, and finds it.
8 - The IconLoader attaches itself to the CachedResource as a CachedResourceClient. CachedResource schedules a timer to deliver callbacks to the IconLoader asynchronously
9 - Before that timer fires, the Frame navigates, so the DocumentLoader detaches itself from the frame.
10 - The timer fires, giving the data to the IconLoader and telling it that it finished.
11 - The IconLoader tells the DocumentLoader it finished, which then tries to call out to the FrameLoader client, but the m_frame is gone.

I'm 97% sure this is how this is happening, but cannot reproduce.

The timing around steps 8-10 is REALLY tight, and I have not found a way to reproduce - it's just a few tight spins of the runloop. 

I'm going to spend a little while longer trying to reproduce before I give up and fix this speculatively.

[Brady Eidson]

Retitling: Cleanup IconLoader stuff when a DocumentLoader detaches from its frame

[Brady Eidson]

Created attachment 313322 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 313322 [details]
Patch

Clearing flags on attachment: 313322

Committed r218502: <http://trac.webkit.org/changeset/218502>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.