Reported by James Pearson as:
boot to run level 3
if not root, then make sure /dev/console is writeable
login and type:
setterm -blank 0
start X
type into an xterm:
while true; do echo "" > /dev/console; usleep 100000; done
while the above loop is running switch to the text console and back
again (Ctrl-Alt-F1 then Ctrl-Alt-F7)
... and the screen will be shifting (and wrapping) to the left.
This problem stems from continuously writing text to the system console (which
is in KD_TEXT mode) while the foreground console is in KD_GRAPHICS
mode. Somewhere along the way, console printing got confused and omitted the
KD_GRAPHICS/KD_TEXT test. Thus, vgacon attempted to scroll the screen of X,
which causes X to shift.
Fix by disallowing vgacon to touch the hardware when the vc is in KD_GRAPHICS
mode. A definitive fix entails a full audit of the console code.
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2ae8547775