ubuntu-x-swat team mailing list archive

[Marcus Haslam <marcus.haslam@xxxxxxxxxxxxx>]

I'm out of the office until 1st August.

On 28 Apr 2011, at 20:52, Bryce Harrington <124406@xxxxxxxxxxxxxxxxxx>  
wrote:

> Heh, I see my comment about this being a minor annoyance got people  
> in a
> huff.  ;-)
>
> Anyway, as to whether it's a kernel or X problem, it's sort of a bit  
> of
> both.  (The best bugs live in the cracks between two codebases.)  X  
> and
> the kernel communicate key events as signals rather than via  
> threading.
> And it only handles one signal at a time, so if for some reason the  
> key
> up signal was fired while another signal was being handled (e.g. from
> another device in your system) then it can get lost.  That's why  
> hitting
> a key a second time (to fire a new up-key signal) makes things work.
> The way signals behave is a kernel thing, so this is why it's partly
> kernel, partly X.  Essentially it's a race condition.  For deeper
> information see http://ajaxxx.livejournal.com/62378.html
>
> Really, it sounds like it's an upstream design flaw in X.  Ajax  
> appears
> to be thinking that the whole system should be ripped out and replaced
> with a threading system.  My own experience with threading is that
> sometimes the cure can be worse than the disease... threading can be
> quite hard to get right and sometimes has nasty side effects.  
>  Needless
> to say, such a change is not trivial and not something we'd do at the
> Ubuntu distro level - definitely work that needs done upstream.  Maybe
> Wayland will gain a better system for handling keyboard events, and
> that's where efforts today should be directed?  Don't know.
>
> As an aside, you guys are right that there could conceivably be some
> rare scenarios where this bug could cause some severe issue like a  
> stuck
> delete key deleting files or whatnot.  Maybe some of you have even
> experienced something like that.  But for the vast majority of cases,
> the issue will exhibit itself as extraneous characters when you're
> typing documents and some such - definitely a lot less severe than
> random GPU lockups or sudden X crashes back to the login screen or  
> your
> monitor suddenly turning tie died.  These latter issues are
> unfortunately not as uncommon as I'd like, and until they are I tend  
> to
> judge anything less severe as a "minor annoyance".  ;-)
>
> But annoyances are bad.  While I don't think this issue is one we're
> likely to work on in Ubuntu at the distro level, I can give some  
> advice
> about how to go forward with it, if you're wanting to pursue it
> yourself.  (And FSM bless you!)
>
> Due to the nature of the issue, it's frequency and severity are  
> going to
> vary from hardware to hardware.  Due to timings in hardware interrupts
> and signal generation, and even interactions with software, you might
> see it only with a particular combination of keyboard, motherboard,  
> and
> mouse.  Or it might go away after turning off your wireless.  Or might
> go away for 3 Ubuntu releases and then suddenly and quite mysteriously
> reappear.  Most of our typical keyboard debugging tools such as xev  
> are
> going to be of limited value in investigating it; it may tell you that
> the release signal didn't show up, but that doesn't explain why.  
>  There
> are kernel debugging interfaces that will show what's going on there,
> but that gives limited insights as well.
>
> The first thing I would look at is obtaining a reliable repetitive  
> test
> case.  Get together hardware and a set of steps that lets you reliably
> reproduce the issue on command, or with a sane enough frequency (like
> steps that let you reproduce >25% of the time).  This makes testing  
> less
> time consuming and also gives you a strong way to determine it's
> definitely fixed.
>
> Next, it would be smart to ensure someone hasn't already fixed it.  
>  That
> could save you a lot of work.  We provide xorg-edgers and kernel  
> ppas to
> facilitate doing this.  See https://launchpad.net/~xorg-
> edgers/+archive/ppa and http://kernel.ubuntu.com/~kernel-ppa/ 
> mainline/.
>
> Finally the hard part, which will require code hacking.  Touch base
> about this with Ajax to find if he has any experimental branches, or  
> if
> he knows if anyone else is working on the problem, and how you can  
> help.
> From his blog post, it sounds like the implementation of threaded  
> input
> handling might be the real way forward, and that could probably  
> benefit
> from extra testers and/or coders.
>
> -- 
> You received this bug notification because you are a member of
> Papercutters, which is subscribed to One Hundred Paper Cuts.
> https://bugs.launchpad.net/bugs/124406
>
> Title:
>  Keyboard keys get stuck and repeat
>
> Status in GNU Emacs:
>  Invalid
> Status in One Hundred Paper Cuts:
>  Invalid
> Status in The Linux Kernel:
>  Confirmed
> Status in X.Org X server:
>  In Progress
> Status in “linux” package in Ubuntu:
>  Won't Fix
> Status in “xorg-server” package in Ubuntu:
>  Triaged
> Status in “linux” source package in Jaunty:
>  Won't Fix
> Status in “xorg-server” source package in Jaunty:
>  Invalid
> Status in Gentoo Linux:
>  New
>
> Bug description:
>  Keyboard keys such as the arrows, Alt-F4, PageUp/PageDown, etc. often
>  get 'stuck' and continue being 'clicked' even after they are
>  physically released. For example when clicking Alt-F4, sometimes it
>  gets stuck so all the windows are closed instead of just one.
>
>  My configuration is Feisty + Xgl + Compiz Fusion. My previous
>  configuration was Edgy + Xgl + Beryl, where this didn't happen.  
> Others
>  have reported the same problem without using either Xgl or Compiz.
>
>  The keyboard itself isn't the problem. When dual-booting to Windows,
>  everything works fine. Also, the problem happens with two different
>  keyboards (internal laptop, external USB).
>
>  My best guess is that the problem occurs at time of high system load.
>  Somehow during these times the key-release signal gets lost and the
>  key-press is repeated indefinitely. This happens more often with
>  Compiz configurations because Compiz tends to increase system load.  
> It
>  also happens more often with power-hungry apps like Firefox and
>  Acrobat Reader for similar reasons.
>
>  PS: When the keys would repeat all input devices would be locked up.
>  ie. mouse won't move, clicks don't do anything, keyboard presses  
> don't
>  register. Then when it becomes unstuck, the mouse moves around and
>  everything. Hope this helps.
>
>  See also this forum thread for other people with the same problem:
>  http://ubuntuforums.org/showthread.php?t=432057


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https://bugs.launchpad.net/bugs/124406

Title:
  Keyboard keys get stuck and repeat

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