X crashing the system
Posted Jul 23, 2004 11:30 UTC (Fri) by
dmantione (guest, #4640)
In reply to:
X crashing the system by giraffedata
Parent article:
Kernel Summit: Video Drivers
There are several things that can go wrong.
The first is quite obvious, if the X-server crashes, the video hardware is in an
unknown state. I.e. the console subsystem of the kernel is unable to draw
anything on the display. A good framebuffer driver might help here by the way,
but the matter of the fact is that the framebuffer devices do not reset all
graphics card registers the X-server uses. The kernel then still thinks the
console is in graphics mode, the keyboard is in full raw mode and therefore
both your display and keyboard are unusable. The system might not have
crashed in the literal sense of the word, but it is unusable.
Second, the X-server mmaps /dev/mem. Therefore the X-server has access to
physical memory. If can of a bug, the X-server can write into random memory.
Even kernel memory is possible.
The X-server also messes with clocks. Personal experience is that clocks are
very dangerous. Graphics chips block the PCI/AGP-bus if their clock signal
malfunctions, causing a lock up of the entire system. My own experience is
that you can get a crash even if you program completely valid values into the
clock registers, because the clock signal can get unstable for a few cycles.
The X-server also does a lot of tweaking on the PCI-bus, which is not very
safe either.
And there are propably still a few more ways the X-server can crash the
computer.
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