Re: [PATCH v2 07/12] ptrace: Don't change __state

Peter Zijlstra
2022-04-29T22:27:55Z

On Fri, Apr 29, 2022 at 04:48:32PM -0500, Eric W. Biederman wrote:
> Stop playing with tsk->__state to remove TASK_WAKEKILL while a ptrace
> command is executing.
>
> Instead TASK_WAKEKILL from the definition of TASK_TRACED, and
> implemention a new jobctl flag TASK_PTRACE_FROZEN. This new This new
> flag is set in jobctl_freeze_task and cleared when ptrace_stop is
> awoken or in jobctl_unfreeze_task (when ptrace_stop remains asleep).
>
> In singal_wake_up add __TASK_TRACED to state along with TASK_WAKEKILL
> when it is indicated a fatal signal is pending. Skip adding
> __TASK_TRACED when TASK_PTRACE_FROZEN is not set. This has the same
> effect as changing TASK_TRACED to __TASK_TRACED as all of the wake_ups
> that use TASK_KILLABLE go through signal_wake_up.
>
> Don't set TASK_TRACED if fatal_signal_pending so that the code
> continues not to sleep if there was a pending fatal signal before
> ptrace_stop is called. With TASK_WAKEKILL no longer present in
> TASK_TRACED signal_pending_state will no longer prevent ptrace_stop
> from sleeping if there is a pending fatal signal.
>
> Previously the __state value of __TASK_TRACED was changed to
> TASK_RUNNING when woken up or back to TASK_TRACED when the code was
> left in ptrace_stop. Now when woken up ptrace_stop now clears
> JOBCTL_PTRACE_FROZEN and when left sleeping ptrace_unfreezed_traced
> clears JOBCTL_PTRACE_FROZEN.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> include/linux/sched.h | 2 +-
> include/linux/sched/jobctl.h | 2 ++
> include/linux/sched/signal.h | 8 +++++++-
> kernel/ptrace.c | 21 ++++++++-------------
> kernel/signal.c | 9 +++------
> 5 files changed, 21 insertions(+), 21 deletions(-)

Please fold this hunk:

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6310,10 +6310,7 @@ static void __sched notrace __schedule(u

/*
* We must load prev->state once (task_struct::state is volatile), such
- * that:
- *
- * - we form a control dependency vs deactivate_task() below.
- * - ptrace_{,un}freeze_traced() can change ->state underneath us.
+ * that we form a control dependency vs deactivate_task() below.
*/
prev_state = READ_ONCE(prev->__state);
if (!(sched_mode & SM_MASK_PREEMPT) && prev_state) {