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/20220421150248.667412...@infradead.org
Eric
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