Created attachment 176251 [details] photo of panic A file system with no problems booting 4.0.1 and 3.9.7 kernels on ancient i686 hardware. Btrfs check has no complaints. But it won't boot 4.1.0.rc2 at all and explodes so spectacularly I can't really capture anything. The best I have so far is using rd.break=pre-mount, and manually mounting the btrfs. No complaints. But the instant I try to write a file: dmesg > dmesg.txt, I get a panic. All I have at the moment is a photo until I can reproduce in a VM.
Created attachment 176261 [details] console Captured with virsh console, x86_64 kvm/qemu VM using Fedora 22 i686 and kernel-4.1.0-0.rc2.git3.1.fc23.i686. If I boot kernel-4.0.0-1.fc22.i686 the problem doesn't happen.
Results are the same whether it's 32bit Pentium M baremetal, or an x86_64 kvm/qemu VM, running 4.1.0-0.rc2.git3.1.fc23.i686. However, if I run 4.1.0-0.rc2.git3.1.fc23.x86_64 on either x86_64 baremetal or the same VM, the problem does not occur.