X crashes when using a zaphod config while more than two GPUs are present.
Submitted by MichaelLong
Assigned to Xorg Project Team
Description
Created attachment 112775 Xorg.0.log with backtrace
My desktop system is configured to use a simple zaphod head configuration, first head is dedicated to my monitor, the second head is a TV. The config is bound to an AMD Radeon HD 5430 card.
I'm also operating vga-passthrough VMs by using KVM/qemu on that system.
A second GPU (GeForce GTX 980) is mainly dedicated for this purpose. There are NO related nouveau/NVIDIA kernel and X components (DDX, mesa etc. ) installed.
So far this setup works great.
Now when I install a third GPU, no matter it is an additional NVIDIA based or AMD based GPU, the X Server instance crashes.
(Side note: AMD based GPUs are stubbed out with pci-stub using the kernel command line to make sure those cards are not picked up by X accidentally).
I noticed this behavior only when using a zaphod config, removing any xorg configs everthing is working.
Kernel: 3.18.x X.Org X Server: 1.15.2
Attachment 112775, "Xorg.0.log with backtrace":
Xorg.0.log