Messages in this thread | | | Date | Thu, 19 May 2011 18:32:46 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 10/10] ptrace: implement group stop notification for ptracer |
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On 05/16, Tejun Heo wrote: > > When group stop state of a seized tracee changes, JOBCTL_TRAP_NOTIFY > is set, which triggers STOP trap but is sticky until the next > PTRACE_GETSIGINFO.
I simply can't understand this patch. And the supposed API as it seen by the user-space. I'll try to read it again and think more.
A couple of questions,
> +static void ptrace_trap_notify(struct task_struct *t) > +{ > + siginfo_t *si = t->last_siginfo; > + > + WARN_ON_ONCE(!(t->ptrace & PT_SEIZED)); > + assert_spin_locked(&t->sighand->siglock); > + > + /* > + * @t is being ptraced and new SEIZE behavior is in effect. > + * Schedule sticky trap which will clear on the next GETSIGINFO. > + */ > + t->jobctl |= JOBCTL_TRAP_NOTIFY;
This is also set by do_signal_stop(). Cleared by PTRACE_GETSIGINFO.
How can this work? Doesn't this mean PTRACE_GETSIGINFO becomes mandatory before PTRACE_CONT? IOW, unless the tracee does PTRACE_GETSIGINFO to clear this bit, PTRACE_CONT just leads to another trap, no?
> + if (task_is_traced(t) && si && si->si_code == PTRACE_STOP_SI_CODE) {
OK, this PTRACE_STOP_SI_CODE check is clear. But the same check in ptrace_check_attach() looks confusing, why can't we set BLOCK_NOTIFY unconditionally?
> + t->jobctl |= JOBCTL_TRAPPING; > + if (!(t->jobctl & JOBCTL_BLOCK_NOTIFY)) > + signal_wake_up(t, true);
Could you please remind me why we can't avoid the awful ptrace_wait_trapping() in do_wait() paths? Assuming that ptrace_check_attach() does this. I got lost a bit.
So. The tracee reports PTRACE_EVENT_STOP, debugger issues a lot of PTRACE_ requests. The tracee can report another trap "in between". Looks confusing... Perhaps I need to get used to it.
Oleg.
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