[PATCH 0/9] ptrace: cleaning up ptrace_stop

[Eric W. Biederman]

While looking at how ptrace is broken on PREEMPT_RT I realized
that ptrace_stop would be much simpler and more maintainable
if tsk->ptrace, tsk->parent, and tsk->real_parent were protected
by siglock.  Most of the changes are general cleanups in support
of this locking change.

While making the necessary changes to protect tsk->ptrace with
siglock I discovered we have two architectures xtensa and um
that were using tsk->ptrace for what most other architectures
use TIF_SIGPENDING for and not protecting tsk->ptrace with any lock.

By the end of this series ptrace should work on PREEMPT_RT with the
CONFIG_FREEZER and CONFIG_CGROUPS disabled, by the simple fact that the
ptrace_stop code becomes less special.  The function cgroup_enter_frozen
because it takes a lock which is a sleeping lock on PREEMPT_RT with
preemption disabled definitely remains a problem.  Peter Zijlstra has
been rewriting the classic freezer and in earlier parts of this
discussion so I presume it is also a problem for PREEMPT_RT.

Peter's series rewriting the freezer[1] should work on top of this
series with minimal changes and patch 2/5 removed.

Eric W. Biederman (9):
      signal: Rename send_signal send_signal_locked
      signal: Replace __group_send_sig_info with send_signal_locked
      ptrace/um: Replace PT_DTRACE with TIF_SINGLESTEP
      ptrace/xtensa: Replace PT_SINGLESTEP with TIF_SINGLESTEP
      signal: Protect parent child relationships by childs siglock
      signal: Always call do_notify_parent_cldstop with siglock held
      ptrace: Simplify the wait_task_inactive call in ptrace_check_attach
      ptrace: Use siglock instead of tasklist_lock in ptrace_check_attach
      ptrace: Don't change __state

 arch/um/include/asm/thread_info.h |   2 +
 arch/um/kernel/exec.c             |   2 +-
 arch/um/kernel/process.c          |   2 +-
 arch/um/kernel/ptrace.c           |   8 +-
 arch/um/kernel/signal.c           |   4 +-
 arch/xtensa/kernel/ptrace.c       |   4 +-
 arch/xtensa/kernel/signal.c       |   4 +-
 drivers/tty/tty_jobctrl.c         |   4 +-
 include/linux/ptrace.h            |   7 --
 include/linux/sched/jobctl.h      |   2 +
 include/linux/sched/signal.h      |   3 +-
 include/linux/signal.h            |   3 +-
 kernel/exit.c                     |   4 +
 kernel/fork.c                     |  12 +--
 kernel/ptrace.c                   |  61 ++++++-------
 kernel/signal.c                   | 187 ++++++++++++++------------------------
 kernel/time/posix-cpu-timers.c    |   6 +-
 17 files changed, 131 insertions(+), 184 deletions(-)

[1] https://lkml.kernel.org/r/20220421150248.667412396@infradead.org

Eric