On Thu, May 28, 2020 at 12:45:01AM +0200, Christian Brauner wrote: > On Wed, May 27, 2020 at 03:37:58PM -0700, Kees Cook wrote: > > But there's a mapping between pidfd and task struct that is separate > > from task struct itself, yes? I.e. keeping a pidfd open doesn't pin > > struct task in memory forever, right? > > No, but that's an implementation detail and we discussed that. It pins > struct pid instead of task_struct. Once the process is fully gone you > just get ESRCH. Oh right! struct pid, yes. Okay, that's quite a bit smaller. > For example, fds to /proc/<pid>/<tid>/ fds aren't just closed once the > task has gone away, userspace will just get ESRCH when it tries to open > files under there but the fd remains valid until close() is called. > > In addition, of all the anon inode fds, none of them have the "close the > file behind userspace back" behavior: io_uring, signalfd, timerfd, btf, > perf_event, bpf-prog, bpf-link, bpf-map, pidfd, userfaultfd, fanotify, > inotify, eventpoll, fscontext, eventfd. These are just core kernel ones. > I'm pretty sure that it'd be very odd behavior if we did that. I'd > rather just notify userspace and leave the close to them. But maybe I'm > missing something. Well, they have a "you are now disconnected" state, which I was thinking could be done entirely entirely on the VFS side of things, but it looks like it's not. So, yes, okay, thank you for walking me through all that. I still want to take a closer look at all the notify calls in here. It seems strange that seccomp has to do all the wakeups (but I guess there are no "generic" poll helpers?) -- Kees Cook _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
