X crashes when using a zaphod config while more than two GPUs are present.
Submitted by MichaelLong
Assigned to Xorg Project Team
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":