Bug 86451

Summary: PC becomes unresponsive to input (and some output) devices, chvt hangs
Product: Process Management Reporter: Nicolas Hillegeer (nicolas)
Component: SchedulerAssignee: Ingo Molnar (mingo)
Status: RESOLVED CODE_FIX    
Severity: high CC: alan, rodrigo.vivi
Priority: P1    
Hardware: x86-64   
OS: Linux   
Kernel Version: 3.17.1 Subsystem:
Regression: No Bisected commit-id:
Attachments: dmesg error output after "sudo chvt N"

Description Nicolas Hillegeer 2014-10-16 23:42:55 UTC 
First of: I have no idea if "Process Management" is the right topic to put this under, since I don't know what's causing this. I'm also having a hard time debugging this as the kernel doesn't print out anything that would signify that it knows something is wrong. Please change it if need be.

I recently upgraded from 3.15.8 to 3.17.1 and found that everything works fine, except that after a while, the system partially freezes.

I say partially because I can still connect with ssh and do a lot of things, such as edit text, run htop, reboot, ...

However, the input devices (such as the keyboard and the mouse) don't respond anymore, and the screen appears frozen as well. Sometimes the mouse still responds (and the cursor moves across the screen) but the keyboard presumably doesn't.

Neither dmesg nor Xorg.0.log show anything out of the ordinary (no errors at all).

I couldn't use my keyboard to perform ctrl+alt+f1 to switch to the VT and try something there because the keyboard is unresponsive. So I thought I was being clever and logged in via ssh then executed "sudo chvt 1". This seemed to hang for quite a long time (a few minutes at least) and to my surprise did finish after a while. However, there was no VT greeting me, the screen stayed unresponsive.

How do I proceed to debug this issue?
Comment 1 Nicolas Hillegeer 2014-10-16 23:48:19 UTC 
Created attachment 154061 [details]
dmesg error output after "sudo chvt N"

Speaking of the devil, I *think* that the "sudo chvt 1" (and multiple "sudo chvt N"'s I issued afterwards, which returned instantaneously) provoked some kind of crash, because  I get some output on dmesg. See attachment.
Comment 2 Rodrigo Vivi 2014-10-17 23:49:09 UTC 
https://bugs.freedesktop.org/show_bug.cgi?id=82612

Fixed-by: 
commit 9c787942907face82da505c2c5493998b56cfc5a
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Fri Sep 5 07:13:25 2014 +0100

    drm/i915: Decouple the stuck pageflip on modeset
    
    If we successfully confuse the hardware, and cause it to drop a queued
    pageflip, we wait for 60s and issue a warning before continuing on with
    the modeset. However, this leaves the pending pageflip still stuck
    indefinitely. Pretend to userspace that it does complete, and let us
    start afresh following the modeset.