KGDB/KDB treats WARN*() as Oops on x86 since 4.12

[Ilya Dryomov]

Hi Jason,

Starting with 4.12, WARN*() is implemented with ud0, generating an
Invalid Opcode exception.  KGDB/KDB gets entered as if it were an Oops,
making KGDB/KDB rather hard to use, particularly on testing kernels.

Alexander posted a fix a while back, but Peter seems to be waiting for
your ack.  Could you please weigh in?

  [PATCH] x86/debug: Handle warnings before the notifier chain
  https://patchwork.kernel.org/patch/9859065/

Thanks,

                Ilya