Dear Christopher, Thanks for your suggestion. I've done a few more experiments before and after updating the BIOS (to the latest version (4105 07/01/2013). Here are the results.
1. Old Bios. Mageia 3 + Fglrx driver => Worked fine 2. Old Bios, Kubuntu Trusty (installed yesterday, fully updated), Open-source (Radeon) driver. => No CPU hang. However, I did have a problem with video-modelines being auto-detected wrongly, (resulting in the monitors showing out-of range. I've since fixed that manually with xrandr --addmode and will shortly file a bug on it, but this is what set me off on the path of trying the binary drivers). 3. Old Bios, Trusty, and the fglrx driver (both fglrx and fglrx-update, as per https://help.ubuntu.com/community/BinaryDriverHowto/AMD ) => CPIU hang. 4. Old Bios, Utopic alpha, and open-source driver => No cpu hang (but the modeline problem still present) 5. New Bios, Utopic, open-source driver => No cpu hang (but the modeline problem still present) 6. New Bios, Utopic, fglrx CPU hang again (see dmesg attached) Best wishes Richard ** Attachment added: "Dmesg output" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1338177/+attachment/4147183/+files/dmesg.txt -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1338177 Title: BUG: soft lockup - CPU#0 stuck for 23s! [Xorg:1295] Status in “linux” package in Ubuntu: Incomplete Bug description: I've just installed Utopic, and my machine is really slow to boot. ProblemType: KernelOops DistroRelease: Ubuntu 14.10 Package: linux-image-3.15.0-6-generic 3.15.0-6.11 [modified: boot/vmlinuz-3.15.0-6-generic] ProcVersionSignature: Ubuntu 3.15.0-6.11-generic 3.15.0 Uname: Linux 3.15.0-6-generic x86_64 Annotation: Your system might become unstable now and might need to be restarted. ApportVersion: 2.14.4-0ubuntu1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC3: rjn 2642 F.... pulseaudio /dev/snd/controlC2: rjn 2642 F.... pulseaudio /dev/snd/controlC0: rjn 2642 F.... pulseaudio /dev/snd/controlC1: rjn 2642 F.... pulseaudio Date: Sun Jul 6 00:58:31 2014 DuplicateSignature: BUG: soft lockup - CPU#0 stuck for 23s! [Xorg:1295] RIP: 0010:location location ulReadMmRegisterUlongViaAddr+0xc/0x10 [fglrx] Failure: oops HibernationDevice: RESUME=UUID=dd46a6f0-bcb8-4e75-b77d-6158117027ac InstallationDate: Installed on 2014-07-05 (0 days ago) InstallationMedia: Kubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20140703) IwConfig: eth0 no wireless extensions. eth1 no wireless extensions. lo no wireless extensions. MachineType: System manufacturer System Product Name ProcFB: 0 radeondrmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.15.0-6-generic root=UUID=41c3bf4e-49c3-4546-aea6-30a91309679d ro PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon. RelatedPackageVersions: kerneloops-daemon 0.12+git20090217-3ubuntu8 RfKill: SourcePackage: linux Title: BUG: soft lockup - CPU#0 stuck for 23s! [Xorg:1295] UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 10/21/2011 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 0703 dmi.board.asset.tag: To be filled by O.E.M. dmi.board.name: P8Z68-V LX dmi.board.vendor: ASUSTeK Computer INC. dmi.board.version: Rev X.0x dmi.chassis.asset.tag: Asset-1234567890 dmi.chassis.type: 3 dmi.chassis.vendor: Chassis Manufacture dmi.chassis.version: Chassis Version dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0703:bd10/21/2011:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP8Z68-VLX:rvrRevX.0x:cvnChassisManufacture:ct3:cvrChassisVersion: dmi.product.name: System Product Name dmi.product.version: System Version dmi.sys.vendor: System manufacturer To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1338177/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp