selftests/bpf: Do not attach kprobe_multi bench to bpf_dispatcher_xdp_func

Alexei reported crash by running test_progs -j on system
with 32 cpus.

It turned out the kprobe_multi bench test that attaches all
ftrace-able functions will race with bpf_dispatcher_update,
that calls bpf_arch_text_poke on bpf_dispatcher_xdp_func,
which is ftrace-able function.

Ftrace is not aware of this update so this will cause
ftrace_bug with:

  WARNING: CPU: 6 PID: 1985 at
  arch/x86/kernel/ftrace.c:94 ftrace_verify_code+0x27/0x50
  ...
  ftrace_replace_code+0xa3/0x170
  ftrace_modify_all_code+0xbd/0x150
  ftrace_startup_enable+0x3f/0x50
  ftrace_startup+0x98/0xf0
  register_ftrace_function+0x20/0x60
  register_fprobe_ips+0xbb/0xd0
  bpf_kprobe_multi_link_attach+0x179/0x430
  __sys_bpf+0x18a1/0x2440
  ...
  ------------[ ftrace bug ]------------
  ftrace failed to modify
  [<ffffffff818d9380>] bpf_dispatcher_xdp_func+0x0/0x10
   actual:   ffffffe9:7b:ffffff9c:77:1e
  Setting ftrace call site to call ftrace function

It looks like we need some way to hide some functions
from ftrace, but meanwhile we workaround this by skipping
bpf_dispatcher_xdp_func from kprobe_multi bench test.

Reported-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

0 files changed, 0 insertions, 0 deletions