Messages in this thread | | | Date | Wed, 20 Apr 2022 12:20:06 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT |
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On Fri, Apr 15, 2022 at 12:57:56PM +0200, Oleg Nesterov wrote: > On 04/15, Oleg Nesterov wrote: > > > > OK, so far it seems that this patch needs a couple of simple fixes you > > pointed out, but before I send V2: > > > > - do you agree we can avoid JOBCTL_TRACED_FROZEN in 1-2 ? > > > > - will you agree if I change ptrace_freeze_traced() to rely > > on __state == TASK_TRACED rather than task_is_traced() ? > > > > Forgot to say, I think 1/5 needs some changes in any case... > > ptrace_resume() does wake_up_state(child, __TASK_TRACED) but doesn't > clear JOBCTL_TRACED. The "else" branch in ptrace_stop() leaks this flag > too. Perhaps I missed something, I'll reread 1/5 again, but the main > question to me is whether 1-2 actually need the JOBCTL_TRACED_FROZEN flag.
Ok, getting back to this. So I did the change to ptrace_resume(), but I'm not entirely sure I understand the issue with the else branch of ptrace_stop().
My understanding is that if we hit that else branch, we've raced wth __ptrace_unlink(), and that will have done:
if (... || task_is_traced(child)) ptrace_signal_wake_up(child, true);
Which will have done that wakeup and cleared both __state and jobctl.
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