* Christian Brauner: > On Thu, Dec 06, 2018 at 01:30:19PM +0100, Florian Weimer wrote: >> * Christian Brauner: >> >> > /* zombies */ >> > Zombies can be signaled just as any other process. No special error will be >> > reported since a zombie state is an unreliable state (cf. [3]). >> >> I still disagree with this analysis. If I know that the target process >> is still alive, and it is not, this is a persistent error condition >> which can be reliably reported. Given that someone might send SIGKILL >> to the process behind my back, detecting this error condition could be >> useful. > > Apart from my objection that this is not actually a reliable state > because of timing issues between e.g. calling wait and a process > exiting The point is that if you are in an error state, the error state does not go away, *especially* if you do not expect the process to terminate and have not arranged for something calling waitpid on the PID. > I have two more concerns and one helpful suggestion. > First, this is hooking pretty deep into kernel internals. So far > EXIT_ZOMBIE is only exposed in kernel/exit.c and I don't see enough > value to drag all of this into kernel/signal.c > Second, all other signal syscalls don't do report errors when signaling > to zombies as well. They cannot do this reliably because the error state is not persistent: the PID can be reused. So for the legacy interface, a difference in error signaling would just have encouraged a bad programming model. > It would be odd if this one suddenly did. I don't think so. My point is that the FD-based mechanism finally allows to cope with this in a reasonable way. > Third, if this really becomes such a big issue for userspace in the > future that we want to do that work then we can add a flag like > TASKFD_DETECT_ZOMBIE (or some such name) that will allow userspace to > get an error back when signaling a zombie. I can live with that. Thanks, Florian
