Messages in this thread | | | Date | Mon, 25 Apr 2022 20:33:43 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 2/5] sched,ptrace: Fix ptrace_check_attach() vs PREEMPT_RT |
| |
On Mon, Apr 25, 2022 at 04:35:37PM +0200, Oleg Nesterov wrote: > On 04/21, Peter Zijlstra wrote: > > > > +static void clear_traced_quiesce(void) > > +{ > > + spin_lock_irq(¤t->sighand->siglock); > > + WARN_ON_ONCE(!(current->jobctl & JOBCTL_TRACED_QUIESCE)); > > This WARN_ON_ONCE() doesn't look right, the task can be killed right > after ptrace_stop() sets JOBCTL_TRACED | JOBCTL_TRACED_QUIESCE and > drops siglock.
OK, will look at that.
> > @@ -2290,14 +2303,26 @@ static int ptrace_stop(int exit_code, in > > /* > > * Don't want to allow preemption here, because > > * sys_ptrace() needs this task to be inactive. > > - * > > - * XXX: implement read_unlock_no_resched(). > > */ > > preempt_disable(); > > read_unlock(&tasklist_lock); > > - cgroup_enter_frozen(); > > + cgroup_enter_frozen(); // XXX broken on PREEMPT_RT !!! > > + > > + /* > > + * JOBCTL_TRACE_QUIESCE bridges the gap between > > + * set_current_state(TASK_TRACED) above and schedule() below. > > + * There must not be any blocking (specifically anything that > > + * touched ->saved_state on PREEMPT_RT) between here and > > + * schedule(). > > + * > > + * ptrace_check_attach() relies on this with its > > + * wait_task_inactive() usage. > > + */ > > + clear_traced_quiesce(); > > Well, I think it should be called earlier under tasklist_lock, > before preempt_disable() above. > > We need tasklist_lock to protect ->parent, debugger can be killed > and go away right after read_unlock(&tasklist_lock). > > Still trying to convince myself everything is right with > JOBCTL_STOPPED/TRACED ...
Can't do it earlier, since cgroup_enter_frozen() can do spinlock (eg. use ->saved_state).
| |