[PATCH v4 0/12] ptrace: cleaning up ptrace_stop

Eric W. Biederman
2022-05-05T18:25:57Z

The states TASK_STOPPED and TASK_TRACE are special in they can not
handle spurious wake-ups. This plus actively depending upon and
changing the value of tsk->__state causes problems for PREEMPT_RT and
Peter's freezer rewrite.

There are a lot of details we have to get right to sort out the
technical challenges and this is my parred back version of the changes
that contains just those problems I see good solutions to that I believe
are ready.

A couple of issues have been pointed but I think this parred back set of
changes is still on the right track. The biggest change in v4 is the
split of "ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs" into
two patches because the dependency I thought exited between two
different changes did not exist. The rest of the changes are minor
tweaks to "ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs";
removing an always true branch, and adding an early test to see if the
ptracer had gone, before TASK_TRAPPING was set.

This set of changes should support Peter's freezer rewrite, and with the
addition of changing wait_task_inactive(TASK_TRACED) to be
wait_task_inactive(0) in ptrace_check_attach I don't think there are any
races or issues to be concerned about from the ptrace side.

More work is needed to support PREEMPT_RT, but these changes get things
closer.

This set of changes continues to look like it will provide a firm
foundation for solving the PREEMPT_RT and freezer challenges.

Eric W. Biederman (11):
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
ptrace: Remove arch_ptrace_attach
signal: Use lockdep_assert_held instead of assert_spin_locked
ptrace: Reimplement PTRACE_KILL by always sending SIGKILL
ptrace: Document that wait_task_inactive can't fail
ptrace: Admit ptrace_stop can generate spuriuos SIGTRAPs
ptrace: Don't change __state
ptrace: Always take siglock in ptrace_resume

Peter Zijlstra (1):
sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state

arch/ia64/include/asm/ptrace.h | 4 --
arch/ia64/kernel/ptrace.c | 57 ----------------
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/x86/kernel/step.c | 3 +-
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.h | 10 ++-
include/linux/sched/jobctl.h | 8 +++
include/linux/sched/signal.h | 20 ++++--
include/linux/signal.h | 3 +-
kernel/ptrace.c | 87 ++++++++---------------
kernel/sched/core.c | 5 +-
kernel/signal.c | 140 +++++++++++++++++---------------------
kernel/time/posix-cpu-timers.c | 6 +-
20 files changed, 140 insertions(+), 240 deletions(-)

Eric