On Fri, Mar 13, 2015 at 12:57 PM, <j...@joshtriplett.org> wrote: > On Fri, Mar 13, 2015 at 05:21:13PM +0100, Oleg Nesterov wrote: >> Josh, >> >> I'll certainly try to read this series, but not before next week. > > Thanks for looking at it. > >> but a couple of nits right now. >> >> On 03/12, Josh Triplett wrote: >> > >> > When passed CLONE_FD, clone4 will return a file descriptor rather than a >> > PID. When the child process exits, it gets automatically reaped, >> >> And even I have no idea what you are actually doing, this doesn't look >> right, see below. >> >> > +static unsigned int clonefd_poll(struct file *file, poll_table *wait) >> > +{ >> > + struct task_struct *p = file->private_data; >> > + poll_wait(file, &p->clonefd_wqh, wait); >> > + return p->exit_state == EXIT_DEAD ? (POLLIN | POLLRDNORM) : 0; >> > +} >> > + >> > +static ssize_t clonefd_read(struct file *file, char __user *buf, size_t >> > count, loff_t *ppos) >> > +{ >> > + struct task_struct *p = file->private_data; >> > + int ret = 0; >> > + >> > + /* EOF after first read */ >> > + if (*ppos) >> > + return 0; >> > + >> > + if (file->f_flags & O_NONBLOCK) >> > + ret = -EAGAIN; >> > + else >> > + ret = wait_event_interruptible(p->clonefd_wqh, p->exit_state >> > == EXIT_DEAD); >> > + >> > + if (p->exit_state == EXIT_DEAD) { >> >> Again, I simply do not know what this code does at all. But I bet the usage >> of EXIT_DEAD is wrong ;) >> >> OK, OK, I can be wrong. But I simply do not see what protects this >> task_struct >> if it is EXIT_DEAD (in fact even if it is EXIT_ZOMBIE). > > If by "what protects" you mean "what keeps it alive", the file > descriptor holds a reference to the task_struct by calling > get_task_struct when created and put_task_struct when released. > > This wait_event_interruptible pairs with the wake_up_all called from > clonefd_do_notify, which exit_notify calls *after* setting the task to > TASK_DEAD. > > Apart from that, what about what the code is doing isn't clear? > >> > @@ -598,7 +600,9 @@ static void exit_notify(struct task_struct *tsk, int >> > group_dead) >> > if (group_dead) >> > kill_orphaned_pgrp(tsk->group_leader, NULL); >> > >> > - if (unlikely(tsk->ptrace)) { >> > + if (tsk->autoreap) { >> > + autoreap = true; >> >> Debuggers won't be happy. A ptraced task should not autoreap itself. > > A process launching a new process with CLONE_FD is explicitly requesting > that the process be automatically reaped without any other process > having to wait on it. The task needs to not become a zombie, because > otherwise, it'll show up in waitpid(-1, ...) calls in the parent > process, which would break the ability to use this to completely > encapsulate process management within a library and not interfere with > the parent's process handling via SIGCHLD and wait{pid,3,4}.
Wouldn't the correct behavior be to keep it alive as a zombie but *not* show it in waitpid, etc? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/