Thanks for the suggestion. Unfortunately, it's at least as bad with the new kernel; maybe worse.
So first of all, "2nd login" doesn't reproduce the issue 100% reliably after all. I tested one last time with kernel 4.4.0-31, and the same exact problem occurred again, but on the 3rd, not 2nd login. I then rebooted into the new kernel 4.8.0-040800rc2, and was able to reproduce it, but it was after the 3rd *logout.* The machine froze on the black console screen that normally appears just momentarily after the desktop goes away but before the lightdm login screen reappears. After eventually regaining control, I logged in again and the display froze shortly before the desktop was completely drawn, more or less as expected. Unfortunately, this time Ctrl+Alt+F1 had no effect after any length of time. Having neglected to first install sshd, I had to hard reset the machine after 30 minutes or so of waiting. I haven't had that happen with the old kernel, but that could also just be luck. By the way, is it possible this bug should be against Xorg instead? The kernel version on my 14.04 installation is 4.4.0-34, or pretty close to the 4.4.0-31 kernel I'm having issues with. ** Attachment added: "kern.log" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1612895/+attachment/4721919/+files/kern.log ** Tags added: kernel-bug-exists-upstream ** Changed in: linux (Ubuntu) Status: Incomplete => Confirmed -- 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/1612895 Title: Display freezes on 2nd+subsequent logins Status in linux package in Ubuntu: Confirmed Bug description: First boot after a fresh install of 16.04 from the 16.04.1 amd64 desktop ISO, with 'download updates' enabled. This is alongside an existing 14.04 installation, which continues to work flawlessly. In particular, this issue cannot be reproduced there. (I've installed the -lts-xenial kernel package there, so it's version 4.4.0.34.24, but NOT the xorg ones.) The first login on the new system worked fine. After simply logging out and in again, the display freezes just after drawing my user's desktop. (This first time, everything was drawn, but on subsequent attempts the background was black and the top Unity panel was empty.) The mouse cursor is movable, but no button or key presses are recognized. Eventually, I press Ctrl+Alt+F1. The mouse cursor disappears immediately; the display stays frozen and otherwise unchanged. After another two minutes or so of waiting, I am finally dumped to the virtual tty, which works fine. At this point a couple of kernel stack traces appear in dmesg (see below), with timestamps corresponding to "just now," i.e. when the vty switch finally occurred. Switching back to the X vty via Alt+F7 brings me back to the still- frozen display, at which point all I can do is Ctrl+Alt+F1 and wait ~2 minutes again. Stopping, then starting the lightdm service brings me back to a working login screen, but logging in just freezes right back again. Finally, rebooting the system allows me to login to a working desktop exactly once -- logging out and in again reproduces this problem reliably. The full dmesg is attached, but the short version is that stack traces appear in pairs, summarized by the following lines on the first occurrence: [ 242.116429] WARNING: CPU: 2 PID: 2539 at /build/linux-dcxD3m/linux-4.4.0/drivers/gpu/drm/drm_irq.c:1326 drm_wait_one_vblank+0x1b5/0x1c0 [drm]() [ 242.116498] CPU: 2 PID: 2539 Comm: Xorg Not tainted 4.4.0-31-generic #50-Ubuntu and by the following, slightly different ones, on the second and beyond: [ 380.232443] WARNING: CPU: 1 PID: 4173 at /build/linux-dcxD3m/linux-4.4.0/drivers/gpu/drm/i915/intel_display.c:3963 intel_crtc_wait_for_pending_flips+0x1e2/0x240 [i915]() [ 380.232563] CPU: 1 PID: 4173 Comm: Xorg Tainted: G W 4.4.0-31-generic #50-Ubuntu ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: linux-image-4.4.0-31-generic 4.4.0-31.50 [modified: boot/vmlinuz-4.4.0-31-generic] ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13 Uname: Linux 4.4.0-31-generic x86_64 ApportVersion: 2.20.1-0ubuntu2.1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: who 3445 F.... pulseaudio CurrentDesktop: Unity Date: Fri Aug 12 19:51:28 2016 HibernationDevice: RESUME=UUID=2065ee3e-d689-4432-a805-4a7822b06d0e InstallationDate: Installed on 2016-08-13 (0 days ago) InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719) MachineType: LENOVO 4236AR5 ProcFB: 0 inteldrmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-31-generic root=UUID=093a7652-dfb2-4f9e-9ceb-23761b18c8ef ro quiet splash RelatedPackageVersions: linux-restricted-modules-4.4.0-31-generic N/A linux-backports-modules-4.4.0-31-generic N/A linux-firmware 1.157.2 SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 10/31/2011 dmi.bios.vendor: LENOVO dmi.bios.version: 83ET66WW (1.36 ) dmi.board.asset.tag: Not Available dmi.board.name: 4236AR5 dmi.board.vendor: LENOVO dmi.board.version: Not Available dmi.chassis.asset.tag: No Asset Information dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: Not Available dmi.modalias: dmi:bvnLENOVO:bvr83ET66WW(1.36):bd10/31/2011:svnLENOVO:pn4236AR5:pvrThinkPadT420:rvnLENOVO:rn4236AR5:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable: dmi.product.name: 4236AR5 dmi.product.version: ThinkPad T420 dmi.sys.vendor: LENOVO To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1612895/+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
