(In reply to comment #4)
> If I read dmesg correctly, it defaults to agp mode 2 but the bug still
> appears with radeon.agpmode=1. Using radeon.agpmode=-1 avoids the freeze,
> though.
> agpmode=-1 will be slower than the default, won't it? Anything else I can do
> to help with fixing this bug?

does agpmode=4 or 8 help?  agpmode=-1 may be slower, depends on the system and
what you are doing.  AGP is old and was kind of broken by design so I don't
think anyone is going to put much effort into making it work better at this
point.