Oleg Nesterov <oleg@xxxxxxxxxx> writes: > Eric, > > I see another series from you, but I simply failed to force myself to read > it carefully. Because at first glance it makes me really sad, I do dislike > it even if it is correct. Yes, yes, sure, I can be wrong. Will try > tomorrow. Yes. I needed to get my thoughts concrete. I missed fixing the race in zap_other_threads. But overall I think things are moving in a good direction. >> >> I don't know who actually useses PTRACE_O_TRACEEXIT so I don't actually >> know what the implications of changing it are. Let's see... > > And nobody knows ;) This is the problem, even the clear ptrace bugfix can > break something, this happened before and we had to revert the obviously- > correct patches; the bug was already used as feature. Yes that is the challenge of changing userspace. Which is why it helps to test as much of a userspace change as possible. Or to get very clever, and figure out how to avoid the userspace change. So I think it is worth knowing the lldb actually uses PTRACE_O_TRACEEXIT. So we can test at least some programs to verify that all is well. I don't see any way around cleaning up PTRACE_O_TRACEEXIT. As we fundamentally have the non-thread-group-leader exec problem. We have to reap that previous leader thread with release_task. Which means we can't stop for a PTRACE_O_TRACEEXIT. >> If delivering a second SIGKILL > ... >> So userspace can absolutely kill a processes in PTRACE_EVENT_EXIT >> before the tracers find it. >> >> Therefore we are only talking a quality of implementation issue >> if we actually stop and wait for the tracer or not. > > Oh, this is another story, needs another discussion. We really need some > changes in this area, we need to distinguish SIGKILL sent from user-space > and (say) from group-exit, and we need to decide when should we stop. > > But at least I think the tracee should never stop if SIGKILL comes from > user space. And yes ptrace_stop() is ugly and wrong, just look at the > arch_ptrace_stop_needed() check. The problem, again, is that any fix will > be user-visible. The only issue I see is that arch_ptrace_stop() may sleep (sparc and ia64 do as they flush the register stack to memory). As the code may sleep it means we can't set TASK_TRACED until after calling arch_ptrace_stop(). My inclination is to just solve that by saying: if (!sigkill_pending(current)) set_current_task(TASK_TRACED); That removes the special case. We have to handle SIGKILL being delivered immediately after set_current_state in any event. And as we are talking about something that happens on rare architecutres I don't see any problem with tweaking that code at all. It is closely enough related I will fold that into the next version of my patch. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
