[PATCH v2 00/14] Short circuit delivery for coredump signals

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

Oleg's recent patchset tweaking how force_sig_info works has inspired me
to finally push through and update the signal handling to have proper
short circuit deliver for coredump signals.  Everything is just simpler
when coredumps are not such a large special case.

What makes this tricky is coredumps have had their own process
shoot-down logic similar to but separate and different from everything
else in the kernel.  The bulk of this set of changes is merging the
process shoot-down logic that is used for signals and the logic for
coredumps.  So the same process shoot-down logic can be shared.

With the shoot-down logic sorted the rest is quite straight forward.

Oleg when reviewing the first version of this set of changes noticed
that dequeue_exit_signal did not properly handle thread local signal
that trigger a coredump.  To resolve this I have added a few more
cleanups so that I can detect a fatal signal as it is being enqueued
and place it in the shared signal queue.

One of those cleanups is a rewrite of detecting if a signal can be
delivered immediately when sent aka short circuit delivery.  The
processing of signals that will be ignored and signals that will cause a
process to exit without returning to userspace (such as SIGKILL) are
both enhanced.

This set of changes is against v7.2-rc1

 fs/coredump.c                          | 161 +++++++++++++++++----------------
 include/linux/coredump.h               |   4 +
 include/linux/sched/signal.h           |   2 +
 include/linux/sched/task.h             |   1 -
 include/linux/signal_types.h           |   3 -
 include/uapi/asm-generic/signal-defs.h |   1 -
 kernel/exit.c                          |  41 ++-------
 kernel/signal.c                        | 119 +++++++++++++++---------
 mm/oom_kill.c                          |   2 +-
 9 files changed, 171 insertions(+), 163 deletions(-)

Eric W. Biederman (14):
      signal: Generalize posixtimer_queue_sigqueue into enqueue_signal
      signal: Factor out sig_blocked from sig_ignored
      signal: More accurate ignoring of signals based on sig_can_short_circuit
      signal: Use sig_can_short_circuit to improve fatal signal delivery
      signal: Compute the exit_code in get_signal
      signal: In get_signal call do_exit when it is unnecessary to shoot down threads
      signal: Bring down all threads when handling a non-coredump fatal signal
      signal: Move stopping for the coredump from do_exit into get_signal
      signal: Move audit_core_dumps from do_coredump into get_signal
      coredump: In zap_threads complete startup if there is no need to wait
      signal: Use the thread killing in get_signal for coredumps
      exit: Make do_group_exit static
      signal: Dequeue fatal signals
      signal: Short circuit deliver coredump signals

 fs/coredump.c                | 153 ++++++++++++++-------------
 include/linux/coredump.h     |   4 +
 include/linux/sched/signal.h |   2 +
 include/linux/sched/task.h   |   1 -
 kernel/exit.c                |  41 ++------
 kernel/signal.c              | 246 +++++++++++++++++++++++++++++--------------
 mm/oom_kill.c                |   2 +-
 7 files changed, 260 insertions(+), 189 deletions(-)