Re: Bug#929834: Buster/XFCE unlock screen is blank

[Paul Wise]

On Tue, Jun 4, 2019 at 4:12 AM Yves-Alexis Perez wrote:

> My gut feeling is that light-locker just uses codepaths not really used
> otherwise, like vt-switch at the same time as suspend/resume or screen off/on.
> Unfortunately debugging i915 is completely out of my league (and I already
> tried multiple time on other issues).

I suggest reporting this to the Intel developers upstream, they should
be able to diagnose the issue and hopefully provide a fix.

-- 
bye,
pabs

https://wiki.debian.org/PaulWise

Re: Bug#929834: Buster/XFCE unlock screen is blank

[Yves-Alexis Perez]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

On Mon, 2019-06-03 at 12:59 -0700, Russ Allbery wrote:
> Ah, good call.  I was also seeing other problems with the Intel driver in
> combination with light-locker where the monitor resolution would be set to
> some incorrect value after restore from lock.  This would come with kernel
> errors like:
> 
> [drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR* uncleared fifo 
> underrun on pipe B
> [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO 
> underrun
> 
> and then lots and lots of:
> 
> [drm:intel_dp_start_link_train [i915]] *ERROR* Timed out waiting for DP idle 
> patterns

My gut feeling is that light-locker just uses codepaths not really used
otherwise, like vt-switch at the same time as suspend/resume or screen off/on.
Unfortunately debugging i915 is completely out of my league (and I already
tried multiple time on other issues).

Regards,
- -- 
Yves-Alexis
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Re: Bug#929834: Buster/XFCE unlock screen is blank

[Russ Allbery]

Yves-Alexis Perez  writes:

> Actually it seems to me that the bug is a bad interaction with light-
> locker/lightdm locking system (which relies on vt switch) and the Intel
> driver. It only seems to happens on this driver, and I think it's also
> been reproduced just by doing vt-switches (but can't remember where it
> was reported).

Ah, good call.  I was also seeing other problems with the Intel driver in
combination with light-locker where the monitor resolution would be set to
some incorrect value after restore from lock.  This would come with kernel
errors like:

[drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR* uncleared fifo 
underrun on pipe B
[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO 
underrun

and then lots and lots of:

[drm:intel_dp_start_link_train [i915]] *ERROR* Timed out waiting for DP idle 
patterns

-- 
Russ Allbery (r...@debian.org)   

Re: Bug#929834: Buster/XFCE unlock screen is blank

[Yves-Alexis Perez]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

On Mon, 2019-06-03 at 21:55 +0200, Yves-Alexis Perez wrote:
> I noted Andreas raised the severity, but I hope someone has an idea how to fix
> that because I don't.

Also, since it was posted on -devel, I guess there's a bit of exposure: if
some people care about Xfce, by all mean please join the team and give a help,
because right now it's basically on my shoulders, with bits of help here and
there from other (mostly on the packaging side, not really on bug triaging). 

It's been like that since years, and it's not really working fine, especially
when I'm not around. And at that point I'm not comfortable anymore with that
because it more likely that I might be “not around” now than before.

Regards,
- -- 
Yves-Alexis
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Re: Bug#929834: Buster/XFCE unlock screen is blank

[Yves-Alexis Perez]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256

On Fri, 2019-05-31 at 18:32 -0700, Russ Allbery wrote:
> This appears to be a bug in light-locker specifically, which is the
> default screen lock program with XFCE with lightdm.  See, for instance:
> 
> https://github.com/the-cavalry/light-locker/issues/114

Actually it seems to me that the bug is a bad interaction with light-
locker/lightdm locking system (which relies on vt switch) and the Intel
driver. It only seems to happens on this driver, and I think it's also been
reproduced just by doing vt-switches (but can't remember where it was
reported).
> 
> Switching to another greeter from the default gtk-greeter appears to help
> according to that bug, which may mean that the bug is actually in
> lightdm-gtk-greeter.  There doesn't appear to be a Debian bug for this; it
> might be a good idea to open one against light-locker (or, if you confirm
> switching to slick-greeter per that bug, lightdm-gtk-greeter).

There are at least a gazillion bugs against light-locker and lightdm, or xfce.
I tried to at least merge some of them (like #846278) but clearly failed to
identify all of them.

And people are still reporting new ones (or posting to -devel) so clearly they
are hard to spot.

Maybe locking through vt-switch is a bad idea,

I noted Andreas raised the severity, but I hope someone has an idea how to fix
that because I don't.

Regards,
- -- 
Yves-Alexis
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Re: Buster/XFCE unlock screen is blank

[Russ Allbery]

Jonathan Dowland  writes:
> On Sat, Jun 01, 2019 at 09:20:48PM +0200, gregor herrmann wrote:

>> I can't reproduce this in a quick test:
>>
>> Terminal 1: sleep 5 ; notify-send foo
>> Terminal 2: xscreensaver-command -lock
>>
>> No "foo" notification pops up over the screensaver image.
>>
>> (This is with awesome, maybe the story is different for desktop
>> environments.)

> I cannot reproduce it with gnome (1:3.30+1) running in an Xorg session
> (rather than Wayland). Perhaps it has been fixed.

Ah, excellent.  Thank you both!

-- 
Russ Allbery (r...@debian.org)   

Re: Buster/XFCE unlock screen is blank

[Jonathan Dowland]

On Sat, Jun 01, 2019 at 09:20:48PM +0200, gregor herrmann wrote:

I can't reproduce this in a quick test:

Terminal 1: sleep 5 ; notify-send foo
Terminal 2: xscreensaver-command -lock

No "foo" notification pops up over the screensaver image.

(This is with awesome, maybe the story is different for desktop
environments.)


I cannot reproduce it with gnome (1:3.30+1) running in an Xorg session
(rather than Wayland). Perhaps it has been fixed.


--

⢀⣴⠾⠻⢶⣦⠀
⣾⠁⢠⠒⠀⣿⡁ Jonathan Dowland
⢿⡄⠘⠷⠚⠋⠀ https://jmtd.net
⠈⠳⣄ Please do not CC me, I am subscribed to the list.

Re: Buster/XFCE unlock screen is blank

[Theodore Ts'o]

On Sat, Jun 01, 2019 at 06:16:58AM +0530, Raj Kiran Grandhi wrote:
> 
> In a fresh install of Buster with XFCE desktop, locking the screen
> blanks the monitor and the monitor enters a power save state. After
> that, neither moving the mouse nor typing on the keyboard would turn
> the monitor back on.
> I could find two ways to get the display back on:
> 
> 1. Typing the password without any visual feedback (while the monitor
> continues to be in the power save state) unlocks the screen and the user
> session is displayed normally.
> 
> 2. Switching to another VT, say vt1 or vt2 turns the monitor back on
> and on switching
> back to the vt of the original session the unlock prompt is displayed
> normally and the screen can be unlocked.

There's another workaround (which is the one I use):

xset s off

This has other consequences as well, of course, but I tend to suspend
my laptop if it's ever going to be left alone, particularly if it's
running on battery.

And once I found a workaround which worked for my laptop, I was too
lazy to find a more "proper" fix.  :-)

- Ted

Re: Buster/XFCE unlock screen is blank

[Russ Allbery]

Georg Faerber  writes:
> On 19-06-01 11:04:28, Russ Allbery wrote:

>> I did some research on that a while back and ended up not filing a bug
>> about it because it looked relatively pointless.  It appeared to be a
>> deep design choice on both sides, and not something anyone was likely
>> to solve, so I just switched to a desktop-aware locker.

> If I may ask, which one?

light-locker, hence why I know about the bug that started this thread.  :)
(I never filed it as a bug since I didn't mind the workaround.  In
retrospect, I should have.)

Obviously given the discussion here I'm not sure I'd recommend that one.

-- 
Russ Allbery (r...@debian.org)   

Re: Buster/XFCE unlock screen is blank

[Georg Faerber]

Hi Russ, all,

On 19-06-01 11:04:28, Russ Allbery wrote:
> I did some research on that a while back and ended up not filing a bug
> about it because it looked relatively pointless.  It appeared to be a
> deep design choice on both sides, and not something anyone was likely
> to solve, so I just switched to a desktop-aware locker.

If I may ask, which one?

Cheers,
Georg


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Re: Buster/XFCE unlock screen is blank

[Russ Allbery]

gregor herrmann  writes:

> I can't reproduce this in a quick test:

> Terminal 1: sleep 5 ; notify-send foo
> Terminal 2: xscreensaver-command -lock

> No "foo" notification pops up over the screensaver image.

> (This is with awesome, maybe the story is different for desktop
> environments.) 

Yeah, I think it may be DE-related.  I ran into it with Xfce and, IIRC,
GNOME (although it would have been older GNOME).

-- 
Russ Allbery (r...@debian.org)   

Re: Buster/XFCE unlock screen is blank

[gregor herrmann]

On Sat, 01 Jun 2019 11:04:28 -0700, Russ Allbery wrote:

> It's worth noting here that xscreensaver has an IMO serious security
> vulnerability (unless maybe this has been fixed?): because it doesn't
> integrate properly with the desktop, it doesn't hide desktop
> notifications.  

I can't reproduce this in a quick test:

Terminal 1: sleep 5 ; notify-send foo
Terminal 2: xscreensaver-command -lock

No "foo" notification pops up over the screensaver image.

(This is with awesome, maybe the story is different for desktop
environments.) 


Cheers,
gregor

-- 
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Re: Buster/XFCE unlock screen is blank

[Russ Allbery]

Adam Borowski  writes:

> But, the culprit is light-locker.  In general, it's in such a buggy
> state that I believe it shouldn't be in the distribution at all, much
> less a default of any kind.  After it replaced xscreensaver[1] as the
> xfce's dependency, I went into some pretty heated arguments, but then
> stormed off and ignored the issue.

It's worth noting here that xscreensaver has an IMO serious security
vulnerability (unless maybe this has been fixed?): because it doesn't
integrate properly with the desktop, it doesn't hide desktop
notifications.  Desktop notifications will appear above the lock screen.
If you therefore leave a locked computer in some relatively public place
(such as an open plan office at work), you may be exposing things on your
screen that you didn't expect, such as direct messages from some messaging
system that's plugged into desktop notifications.

I did some research on that a while back and ended up not filing a bug
about it because it looked relatively pointless.  It appeared to be a deep
design choice on both sides, and not something anyone was likely to solve,
so I just switched to a desktop-aware locker.

-- 
Russ Allbery (r...@debian.org)   

Re: Buster/XFCE unlock screen is blank

[Holger Levsen]

On Sat, Jun 01, 2019 at 06:29:31PM +0200, Adam Borowski wrote:
> Using unstable myself, I'm not sure what to recommend for Buster.  

https://tracker.debian.org/pkg/physlock


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Re: Buster/XFCE unlock screen is blank

[Jonathan Carter]

Hey Adam

On 2019/06/01 18:29, Adam Borowski wrote:
> At the time of the xscreensaver debacle, there was no sane alternative
> (candidates depended on 80% of GNOME, offered no feedback nor discoverable
> controls to the user, etc).  There _is_ a wonderful alternative now:
> xfce4-screensaver, which seems to work perfectly[2] -- but alas, it's not in
> Buster.

When I first filed the ITP for xfce4-screensaver I got some pushback (of
which I don't all disagree with). After some discussion and digging in
deeper into the issue the Debian Xfce team agreed that it can be
maintained as part of the Xfce team. At freeze time it was still in
alpha and had some show-stopper issues, we decided that it would be best
for everyone not to have that in buster at that time. There are also
still some integration issues that are still outstanding. Overall it
just wasn't ready for buster in time, but I'll be happy to work on a
backport for buster when some of the last few issues have been resolved.

-Jonathan

-- 
  ⢀⣴⠾⠻⢶⣦⠀  Jonathan Carter (highvoltage) 
  ⣾⠁⢠⠒⠀⣿⡁  Debian Developer - https://wiki.debian.org/highvoltage
  ⢿⡄⠘⠷⠚⠋   https://debian.org | https://jonathancarter.org
  ⠈⠳⣄  Be Bold. Be brave. Debian has got your back.

Re: Buster/XFCE unlock screen is blank

[Adam Borowski]

On Sat, Jun 01, 2019 at 11:06:42AM +0200, Andreas Tille wrote:
> > This appears to be a bug in light-locker specifically, which is the
> > default screen lock program with XFCE with lightdm.  See, for instance:
> > 
> > https://github.com/the-cavalry/light-locker/issues/114
> > 
> > Switching to another greeter from the default gtk-greeter appears to help
> > according to that bug, which may mean that the bug is actually in
> > lightdm-gtk-greeter.  There doesn't appear to be a Debian bug for this; it
> > might be a good idea to open one against light-locker (or, if you confirm
> > switching to slick-greeter per that bug, lightdm-gtk-greeter).
> 
> Yes, please file the bug (and may be report the bug number here).  We
> should not release with a broken greeter as default since we can not
> assume that normal users will find out the "switch VT trick" and instead
> will assume the box is frozen. 

While I greatly prefer slick-greeter (I use it exclusively since the first
day I reviewed+sponsored the package), I recall it doesn't support a11y
anywhere as well as the default greeter.  This is old data, though -- as my
wetware doesn't require a11y, I wouldn't even know what to look at.

But, the culprit is light-locker.  In general, it's in such a buggy state
that I believe it shouldn't be in the distribution at all, much less a
default of any kind.  After it replaced xscreensaver[1] as the xfce's
dependency, I went into some pretty heated arguments, but then stormed off
and ignored the issue.

Just some issues with light-locker.  INACCURATE, BASED ON AN OLD VERSION,
AND NOT RESEARCHED WELL AT ALL.  (Ie, areas to look at, not proper reports)
* it doesn't show anyone is logged in -- lock screen is pixel-to-pixel
  identical as the login screen
* breaks when the *DM is not lightdm.  A package dependency doesn't mean
  that lightdm is running or used to start that session.
* breaks with multiseat (as in: concurrent same-uid logins from different
  seats, not the systemd meaning)
* breaks if ssh -X into the box is used with some programs
* breaks with any non-standard VT assignment
(Some of the issues might have been already fixed.)

At the time of the xscreensaver debacle, there was no sane alternative
(candidates depended on 80% of GNOME, offered no feedback nor discoverable
controls to the user, etc).  There _is_ a wonderful alternative now:
xfce4-screensaver, which seems to work perfectly[2] -- but alas, it's not in
Buster.

Using unstable myself, I'm not sure what to recommend for Buster.  But if
the bugs can't get fixed in late freeze, and slick-greeter is not enough,
I's light-locker not the greeter I'd propose switching out of.


Meow!

[1]. When jwz planted a time-bomb in xscreensaver.
[2]. There was an issue with taking lots of CPU even when the monitor has
 been long since powered down, but that's now fixed.
-- 
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Re: Buster/XFCE unlock screen is blank

[Raj Kiran Grandhi]

> > Switching to another greeter from the default gtk-greeter appears to help
> > according to that bug, which may mean that the bug is actually in
> > lightdm-gtk-greeter.  There doesn't appear to be a Debian bug for this; it
> > might be a good idea to open one against light-locker (or, if you confirm
> > switching to slick-greeter per that bug, lightdm-gtk-greeter).

Switching to slick-greeter helped. Thank you.

>
> Yes, please file the bug (and may be report the bug number here).  We
> should not release with a broken greeter as default since we can not
> assume that normal users will find out the "switch VT trick" and instead
> will assume the box is frozen.

Thank you for the feedback. I have filed a bug report (929834) for this issue.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929834

Regards,
Raj Kiran

Re: Buster/XFCE unlock screen is blank

[Andreas Tille]

Hi Russ,

On Fri, May 31, 2019 at 06:32:52PM -0700, Russ Allbery wrote:
> (This probably belonged on debian-user, but since I have background on
> this specific problem and already did the research.)

While this seems to be a problem for debian-user its very sensible that
the issue was raised here as well.  I stumbled upon this issue on two
laptops and I consider this a serious issue for the Buster release that.
Users ending up with a black screen in a not so uncommon setup is
something we need to avoid.  I intended to write a bug report about this
soon.
 
> Raj Kiran Grandhi  writes:
> 
> > In a fresh install of Buster with XFCE desktop, locking the screen
> > blanks the monitor and the monitor enters a power save state. After
> > that, neither moving the mouse nor typing on the keyboard would turn
> > the monitor back on.
> 
> Ctrl-Alt-F7 will also restore the desktop (which I think is just another
> version of your solution 2 of switching VTs).
> 
> This appears to be a bug in light-locker specifically, which is the
> default screen lock program with XFCE with lightdm.  See, for instance:
> 
> https://github.com/the-cavalry/light-locker/issues/114
> 
> Switching to another greeter from the default gtk-greeter appears to help
> according to that bug, which may mean that the bug is actually in
> lightdm-gtk-greeter.  There doesn't appear to be a Debian bug for this; it
> might be a good idea to open one against light-locker (or, if you confirm
> switching to slick-greeter per that bug, lightdm-gtk-greeter).

Yes, please file the bug (and may be report the bug number here).  We
should not release with a broken greeter as default since we can not
assume that normal users will find out the "switch VT trick" and instead
will assume the box is frozen. 

Kind regards

 Andreas.

-- 
http://fam-tille.de

Re: Buster/XFCE unlock screen is blank

[Russ Allbery]

(This probably belonged on debian-user, but since I have background on
this specific problem and already did the research.)

Raj Kiran Grandhi  writes:

> In a fresh install of Buster with XFCE desktop, locking the screen
> blanks the monitor and the monitor enters a power save state. After
> that, neither moving the mouse nor typing on the keyboard would turn
> the monitor back on.

Ctrl-Alt-F7 will also restore the desktop (which I think is just another
version of your solution 2 of switching VTs).

This appears to be a bug in light-locker specifically, which is the
default screen lock program with XFCE with lightdm.  See, for instance:

https://github.com/the-cavalry/light-locker/issues/114

Switching to another greeter from the default gtk-greeter appears to help
according to that bug, which may mean that the bug is actually in
lightdm-gtk-greeter.  There doesn't appear to be a Debian bug for this; it
might be a good idea to open one against light-locker (or, if you confirm
switching to slick-greeter per that bug, lightdm-gtk-greeter).

-- 
Russ Allbery (r...@debian.org)   

Buster/XFCE unlock screen is blank

[Raj Kiran Grandhi]

Hi,

In a fresh install of Buster with XFCE desktop, locking the screen
blanks the monitor and the monitor enters a power save state. After
that, neither moving the mouse nor typing on the keyboard would turn
the monitor back on.
I could find two ways to get the display back on:

1. Typing the password without any visual feedback (while the monitor
continues to be in the power save state) unlocks the screen and the user
session is displayed normally.

2. Switching to another VT, say vt1 or vt2 turns the monitor back on
and on switching
back to the vt of the original session the unlock prompt is displayed
normally and the screen can be unlocked.

For a single user system, this is not a big deal, but is an important
issue if multiple users are logged in simultaneously.

I am not sure to which package this bug belongs to.
The closest I could find online was this:
https://bbs.archlinux.org/viewtopic.php?id=240200 wherein installing
the nouveau video driver appeared to have fixed the issue. However,
that solution is not applicable in my case as I have an integrated
intel graphics controller.

I had discovered this behaviour after a dist-upgrade to buster from
the current stable. I then made a clean install onto a spare hdd using
debian-buster-DI-rc1-amd64-netinst.iso and choosing the XFCE desktop
and am able to reproduce this bug.
Asking around on debian-user, I found a couple of other users who have
also experienced this same issue.

I shall be happy to assist the developers in troubleshooting this
issue. Please let me know if any other info is needed. I am running on
Intel i5-4440 CPU with its integrated graphics controller.

Thank you,
Raj Kiran