[PATCH v5 0/6] Not restarting for due to signals.

[Eric W. Biederman]

This builds on patches 1-15 of my previous patch posting.  As those are
non-controversial I am not posting them again.

I took longer than I had hoped to get this set together because a kernel
testing robot noticed some random corruption with the way I had been
adding to the list.  I finally tracked it down to failing to remove the
sigset from the list during fork_idle.  So I have made that logic
simpler and use hlist_del_init which will only remove an item from a
list if it was placed on the list in the first place.

I took Oleg's suggesting and moved calculate_sigpending into
schedule_tail where recalc_sigpending an be used directly.  Then in
calculate_sigpending I just unconditionally set TIF_SIGPENDING and allow
recalc_sigpending to clear TIF_SIGPENDING if we don't need it.

I also now handle the stop/continue signal magic where we only let one
of stop signals and SIGCONT be pending at a time.  Looking at it from
first principles dropping one of SIGTSTP SIGTTIN SIGTTOU or SIGCONT
before calling it's handler feels wrong.  I checked and it is our
historical behavior, so I won't even thinking of introducing different
behavior at this point.

Eric W. Biederman (6):
      fork: Move and describe why the code examines PIDNS_ADDING
      fork: Unconditionally exit if a fatal signal is pending
      signal: Add calculate_sigpending()
      fork: Skip setting TIF_SIGPENDING in ptrace_init_task
      fork: Have new threads join on-going signal group stops
      signal: Don't restart fork when signals come in.

 include/linux/ptrace.h       |  2 --
 include/linux/sched/signal.h | 11 ++++++++++
 init/init_task.c             |  1 +
 kernel/fork.c                | 49 ++++++++++++++++++++++++++++++--------------
 kernel/sched/core.c          |  2 ++
 kernel/signal.c              | 43 ++++++++++++++++++++++++++++++++++++++
 6 files changed, 91 insertions(+), 17 deletions(-)

Eric