On Wed, Jan 31, 2024 at 11:24:48AM -0800, Andy Lutomirski wrote: > > On 01/31, Oleg Nesterov wrote: > > > > > > On 01/31, Andy Lutomirski wrote: > > > Please note > > > > > > /* TODO: respect PIDFD_THREAD */ > > > > > > this patch adds into pidfd_send_signal(). > > > > > > See also this part of discussion > > > > > > > > + /* TODO: respect PIDFD_THREAD */ > > > > > > > > So I've been thinking about this at the end of last week. Do we need to > > > > give userspace a way to send a thread-group wide signal even when a > > > > PIDFD_THREAD pidfd is passed? Or should we just not worry about this > > > > right now and wait until someone needs this? > > > > > > I don't know. I am fine either way, but I think this needs a separate > > > patch and another discussion in any case. Anyway should be trivial, > > > pidfd_send_signal() has the "flags" argument. > > > > > > with Christian in https://lore.kernel.org/all/20240130112126.GA26108@xxxxxxxxxx/ > > I missed that. Whoops. > > On Wed, Jan 31, 2024 at 11:15 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > Forgot to mention... > > > > And I agree that pidfd_send_signal(flags => PGID/SID) can make > > some sense too. > > > > But this a) doesn't depend on PIDFD_THREAD, and b) needs another > > patch/discussion. > > > > But again, I am not sure I understood you correctly. > > > > Hmm. > > When one works with regular (non-fd) pids / pgids etc, one specifies > the signal domain at the time that one sends the signal. I don't know > what pidfds should do. It seems a bit inefficient for anything that > wants a pidfd and might send a signal in a different mode in the > future to have to hold on to multiple pidfds, so it probably should be > a pidfd_send_signal flag. > > Which leaves the question of what the default should be. Should > pidfd_send_signal with flags = 0 on a PIDFD_THREAD signal the process > or the thread? I guess there are two reasonable solutions: > > 1. flags = 0 always means process. And maybe there's a special flag > to send a signal that matches the pidfd type, or maybe not. > > 2. flags = 0 does what the pidfd seems to imply, and a new > PIDFD_SIGNAL_PID flag overrides it to signal the whole PID even if the > pidfd is PIDFD_THREAD. > > Do any of you have actual use cases in mind where one choice is > clearly better than the other choice? So conceptually I think having the type of pidfd dictate the default scope of the signal is the most elegant approach. And then very likely we should just have: PIDFD_SIGNAL_THREAD PIDFD_SIGNAL_THREAD_GROUP PIDFD_SIGNAL_PROCESS_GROUP I think for userspace it doesn't really matter as long as we clearly document what's going on. Thoughts?
