On Sat, Aug 18, 2018 at 1:17 AM Jakub Wilk <jwilk@xxxxxxxxx> wrote: > > I reproduced this on Linux 4.17. As one would expect, this happens also > with fork(2). > > This seems to contradict the fork(2) man page, which says that EAGAIN is > returned when “the maximum number of PIDs, /proc/sys/kernel/pid_max, was > reached”. I took a look at the fork manpage, which says that EAGAIN can be returned for four reasons - because of pid_max (which seems to be wrong), because of thread-max, because of RLIMIT_NPROC, and because of cgroup pids.max. I checked all of these cases on my clone test program and they all return EAGAIN except for the pid_max case, which returns ENOSPC. The clone(2) docs say that EAGAIN is returned if "Too many process are already running; see fork(2)", which seems adequate to cover this off. I guess I should submit a second patch to remove pid_max from the list of EAGAIN cases in fork(2) and mention it returns ENOSPC instead?
