Created attachment 25703 [details]
I was doing nothing special and X locked. Mouse cursor wasn't moving. There was message in Xorg.log nor dmesg. Attached is GPU dump.
I'm using Fedora 11 with KMS, Metacity as compositor.
Adjusting severity: crashes & hangs should be marked critical.
Ah, if the mouse cursor wasn't moving it would be a problem with the X Server, so the GPU dump won't show much (in your case: the GPU was completely caught up with rendering). Could you get a backtrace of the server if it happens again, assuming the server was still running?
Also, please include dmesg and Xorg.0.log. Even if you don't see interesting messages in it, it's important for correlating issues.
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