On Sun, Mar 15, 2015 at 03:52:23PM +0100, Oleg Nesterov wrote: > On 03/15, Josh Triplett wrote: > > Add a CLONE_AUTOREAP flag to request this behavior unconditionally, > > Yes, CLONE_AUTOREAP is much better. And I agree (mostly) with that > we should rely on do_notify_parent(). > > Howver the patch still doesn't look right. First of all, ->autoreap > should be per-process, not per-thread. Ah, you're thinking of the case where the parent process launches a child with CLONE_AUTOREAP, that child process launches siblings with CLONE_THREAD and without CLONE_AUTOREAP, and one of those siblings is the last to exit? That seems easy enough to handle: instead of setting ->autoreap unconditionally in copy_process, I can set it only in the non-CLONE_THREAD case, and otherwise let it inherit. Then every task in the group will have the same value for autoreap. (As an aside, what *is* the use case for CLONE_PARENT without CLONE_THREAD?) > And there are ptrace/mt issues, > it seems. Just for example, we should avoid EXIT_TRACE if autoreap in > wait_task_zombie() even if we are going to re-notify parent. I don't see how EXIT_TRACE can happen in wait_task_zombie if autoreap is set. wait_task_zombie does a cmpxchg with exit_state and doesn't proceed unless exit_state was EXIT_ZOMBIE, and I don't see how we can ever reach the EXIT_ZOMBIE state if autoreap. > EXCEPT: do we really want SIGCHLD from the exiting child? I think we > do not. I won't really argue though, but this should be discussed and > documented. IIUC, with your patch it is still sent. I think we do, yes. The caller of clone can already specify what signal they want, including no signal at all. If they specify a signal (SIGCHLD or otherwise) along with CLONE_AUTOREAP, we can send that signal. I don't think that causes any particular problem. That's the same semantic you'd get if you have a SIGCHLD handler with SA_NOCLDWAIT: you'd still get the signal, even though you don't need to (and can't) wait on the child process. > Josh, please give me some time to think and re-check, I'll write another > email next week. I am not sure this is really needed, but it seems to > me that we need the preparation patch to make this change clear/simple. I'd appreciate any feedback you can offer on this series, including any potential subtle interactions with ptrace. - Josh Triplett -- 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
