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  1. Bug #1927076
  2. Comment #22

Comment 22 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])

I was looking at latest changes since 5.11 to powerpc64 BPF JIT and found the following commit:

commit 20ccb004bad659c186f9091015a956da220d615d
Author: Naveen N. Rao <email address hidden>
Date: Wed Jun 9 14:30:24 2021 +0530

    powerpc/bpf: Use bctrl for making function calls

    blrl corrupts the link stack. Instead use bctrl when making function
    calls from BPF programs.

    Reported-by: Anton Blanchard <email address hidden>
    Signed-off-by: Naveen N. Rao <email address hidden>
    Signed-off-by: Michael Ellerman <email address hidden>
    Link: https://<email address hidden>

Though the link stack is unarchitected, that is, it should be transparent to the user aside from branch prediction performance, perhaps there is a bug in the implementation. Considering we have only observed this on POWER8 and with different stack traces, I wouldn't discard the possibility.

As this is not present on 5.13 either, I am building a test kernel with a backport so it can be tested.

Cascardo.