[GIT PULL] ptrace: Stop supporting SIGKILL for PTRACE_EVENT_EXIT

["Eric W. Biederman" <ebiederm@xmission.com>]

Linus,

Please pull signal-for-v5.20 from the git tree:
  git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git refs/tags/signal-for-v5.20
  HEAD: 9a95f78eab70deeb5a4c879c19b841a6af5b66e7 signal: Drop signals received after a fatal signal has been processed

Recently I had a conversation where it was pointed out to me that
SIGKILL sent to a tracee stropped in PTRACE_EVENT_EXIT is quite
difficult for a tracer to handle.

Keeping SIGKILL working after the process has been killed is pain
from an implementation point of view.

So since the debuggers don't want this behavior let's see if we can
remove this wart for the userspace API

If a regression is detected it should only need to be the last change
that is the reverted.  The other two are just general cleanups that
make the last patch simpler.

Eric W. Biederman (3):
      signal: Ensure SIGNAL_GROUP_EXIT gets set in do_group_exit
      signal: Guarantee that SIGNAL_GROUP_EXIT is set on process exit
      signal: Drop signals received after a fatal signal has been processed

 fs/coredump.c                |  2 +-
 include/linux/sched/signal.h |  1 +
 kernel/exit.c                | 20 +++++++++++++++++++-
 kernel/fork.c                |  2 ++
 kernel/signal.c              |  3 ++-
 5 files changed, 25 insertions(+), 3 deletions(-)