The Ubuntu-power-systems project

  1. Bug #1927076
  2. Comment #30

Comment 30 for bug 1927076

Revision history for this message
Thadeu Lima de Souza Cascardo (cascardo) wrote : Re: IPv6 TCP in reuseport_bpf_cpu from ubuntu_kernel_selftests/net crash P8 node entei on 5.8 kernel (Oops: Exception in kernel mode, sig: 4 [#1])

About this latest comment. So, CPU #0 has crashed at pc = c008000013566eb8, its ctr and r12 match, same as usual, it was called by __bpf_prog_run_save_cb as the BPF JITed program. Dumping the program from CPU #0 perspective, it has traps at that address.

It turns out the JIT fills up a whole page with traps and puts the JITed BPF program on a random offset of that page (look at kernel/bpf/core.c:bpf_jit_binary_alloc).

When we go to the hotplugged CPU, however, CPU #9f (159), that same page looks different, with the code placed where it was expected.

Still, it looks like fp->aux->jit_data is NULL on both CPUs, which is not as expected.

I am wondering if either the icache is not being flushed properly, or RCU is not operating correctly. As other issues are not seen, more likely something related to the icache. But I don't see any IPIs involved when flushing the icache, so possibly firmware or micro-architecture related?

Cascardo.