On Thu, Dec 06, 2018 at 05:39:18PM -0800, Daniel Colascione wrote: > On Thu, Dec 6, 2018 at 4:59 PM Serge E. Hallyn <serge@xxxxxxxxxx> wrote: > > > > On Thu, Dec 06, 2018 at 04:34:54PM -0800, Daniel Colascione wrote: > > > On Thu, Dec 6, 2018 at 4:31 PM Serge E. Hallyn <serge@xxxxxxxxxx> wrote: > > > > > > > > On Fri, Dec 07, 2018 at 12:17:45AM +0100, Christian Brauner wrote: > > > > > On Thu, Dec 06, 2018 at 11:39:48PM +0100, Christian Brauner wrote: > > > > > > On Thu, Dec 06, 2018 at 03:46:53PM -0600, Eric W. Biederman wrote: > > > > > > > Christian Brauner <christian@xxxxxxxxxx> writes: > > > > > > > > > > > > > > >> Your intention is to add the thread case to support pthreads once the > > > > > > > >> process case is sorted out. So this is something that needs to be made > > > > > > > >> clear. Did I miss how you plan to handle threads? > > > > > > > > > > > > > > > > Yeah, maybe you missed it in the commit message [2] which is based on a > > > > > > > > discussion with Andy [3] and Arnd [4]: > > > > > > > > > > > > > > Looking at your references I haven't missed it. You are not deciding > > > > > > > anything as of yet to keep it simple. Except you are returning > > > > > > > EOPNOTSUPP. You are very much intending to do something. > > > > > > > > > > > > That was clear all along and was pointed at every occassion in the > > > > > > threads. I even went through the hazzle to give you all of the > > > > > > references when there's lore.kernel.org. > > > > > > > > > > > > > > > > > > > > Decide. Do you use the flags parameter or is the width of the > > > > > > > target depending on the flags. > > > > > > > > > > Ok, let's try to be constructive. I understand the general concern for > > > > > the future so let's put a contract into the commit message stating that > > > > > the width of the target aka *what is signaled* will be based on a flag > > > > > parameter if we ever extend it: > > > > > > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PGID); > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_TID); > > > > > > > > > > with the current default being > > > > > > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PID); > > > > > > > > > > This seems to me the cleanest solution as we only use one type of file > > > > > descriptor. Can everyone be on board with this? If so I'm going to send > > > > > out a new version of the patch. > > > > > > > > > > Christian > > > > > > > > I'm on board with this, but I think you need to also clarify what exactly > > > > the fd stands for. I think that (a) userspace should not have to care > > > > about the struct pid implementation, and so (b) the procfd should stand > > > > for all the pids. So when taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PGID) > > > > becomes implemented, then open(/proc/5) will pin all three pids, as will > > > > open(/proc/5/task/6). > > > > > > This change doesn't "pin" any PID, and it makes no sense to make a > > > process FD stand for all its threads. What does that even mean? > > > > Currently the patch relies on the procfd inode saving a copy to the PIDTYPE_PID > > pid. > > struct pid doesn't have a type field. The interpretation depends on > the caller's use of the struct pid, and in the current path, that's > PIDTYPE_PID. What, specifically, is wrong with the current approach? > > > I'm not sure offhand, can it go to the PIDTYPE_PGID from that after the > > task has died, or not? I didn't think so. If it can then great. > > You're arguing that something that does, in fact, work, is somehow > broken in some unspecified way. The kill_pid_info lookup works fine. > What, specifically, is wrong with the semantics as implemented? > > > The point is (a) these are details which should not have to bother userspace, > > These details *don't* bother userspace. > > You're raising concerns that are either imaginary or long-since > addressed. Does the patch cause some kind of maintenance burden? No, > it doesn't, not moreso than any other piece of code. Does the > interface have unclear semantics? No, it clearly sends a signal to a > process, just like kill. Does the patch expose kernel implementation > details? No, it doesn't, because the interface is simply not defined > in terms of these details. Do we need to change how signal delivery > works? No, because if it's fine for kill, it's fine for this facility, > and if some future signal cleanup separates the cases more, that > cleanup can change this code as well. > > The change is well-documented, simple, extensible, and addresses an > actual problem. Every legitimate technical criticism has now been > addressed. I don't understand where this opposition is coming from, > since the objections refer to nothing that's actually in the patch or > exposed to the user. > > > and (b) how to decide who we're sending the signal to (tid/pid/pgid) should > > be specified in precisely one way. So either a flag, or comign from the type > > of fd that was opened. > > You can't send signals to a thread with the current patch. There's no > ambiguity in providing zero ways to do something. So Serge's point is not about changing the current patch. What he's basically saying is: If we are expected to state how we were to extend this syscall in the future which Serge and I figured is currently Eric's only remaining objection then: - flags are a good way to go (I agree) - there's a concrete way how to do this by stashing the relevent struct pids for PIDTYPE_PID, PIDTYPE_TGID, PIDTYPE_PGID in file->private_data which can then be retrieved in taskfd_send_signal() There is not intent nor requirement to do this right now. What we have right now is fine for a start, I agree! But here's how we go forward if we ever need to! :) Christian
