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Bug#964263: linux-image-5.7.0-1-amd64: Switching from a graphical VT to a non-graphical one freezes display

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Package: src:linux
Version: 5.7.6-1
Severity: normal

Dear Maintainer,

When I switch from a VT running a graphical environment, specifically
EXWM, to a VT running a plain old console with getty, the display
freezes up. Switching from that VT to another one (graphical or console)
unfreezes the display. The VT still recognizes my keypresses, but it
still displays whatever was on the screen before I switched VTs. I use
Ctrl+Alt+F[1-6] to switch VTs.

Strangely enough, this doesn't happen all the time. Sometimes I can't
make it happen even once, but sometimes it happens most of the time. I
have observed the bug in both EXWM and i3, but I have yet to observe it
in GNOME.

I noticed this when I upgraded the kernel, and if I boot onto the old
one (linux-image-amd64 5.6.14-2, linux-image-5.6.0-1-amd64 5.6.7-1), I
am unable to cause the symptoms described.

Also, if the non-graphical VT that I am switching to is not running
getty, the symptoms do not appear. So if I run 'systemctl stop
getty@tty3.service' and then run a graphical shell (using startx) in
tty2, switching from tty2 to tty3 will not freeze the display. However,
if I then switch from tty3 back to tty2 and then back to tty3 again, it
will (maybe) freeze the display, since getty is now running in tty3.

Note that I only stopped getty, I didn't actually deallocate the VT
(using deallocvt). I suspect that stopping getty could have caused the
VT to automatically deallocate itself.

I have not observed this bug when switching from a graphical to
graphical VT, from a non-graphical to non-graphical VT, or from a
non-graphical to graphical VT. Only when switching from a graphical to
non-graphical VT does the bug appear.

Thanks,
Asher

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Bug#964263: linux-image-5.7.0-1-amd64: Switching from a graphical VT to a non-graphical one freezes display Asher Gordon <AsDaGo@posteo.net> - 2020-07-04 19:30 +0200

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