From 10dab84caf400f2f5f8b010ebb0c7c4272ec5093 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Sun, 8 Mar 2020 14:29:17 +0100 Subject: pid: make ENOMEM return value more obvious The alloc_pid() codepath used to be simpler. With the introducation of the ability to choose specific pids in 49cb2fc42ce4 ("fork: extend clone3() to support setting a PID") it got more complex. It hasn't been super obvious that ENOMEM is returned when the pid namespace init process/child subreaper of the pid namespace has died. As can be seen from multiple attempts to improve this see e.g. [1] and most recently [2]. We regressed returning ENOMEM in [3] and [2] restored it. Let's add a comment on top explaining that this is historic and documented behavior and cannot easily be changed. [1]: 35f71bc0a09a ("fork: report pid reservation failure properly") [2]: b26ebfe12f34 ("pid: Fix error return value in some cases") [3]: 49cb2fc42ce4 ("fork: extend clone3() to support setting a PID") Signed-off-by: Christian Brauner --- kernel/pid.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'kernel/pid.c') diff --git a/kernel/pid.c b/kernel/pid.c index 19645b25b77c..647b4bb457b5 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -247,6 +247,14 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid, tmp = tmp->parent; } + /* + * ENOMEM is not the most obvious choice especially for the case + * where the child subreaper has already exited and the pid + * namespace denies the creation of any new processes. But ENOMEM + * is what we have exposed to userspace for a long time and it is + * documented behavior for pid namespaces. So we can't easily + * change it even if there were an error code better suited. + */ retval = -ENOMEM; if (unlikely(is_child_reaper(pid))) { -- cgit v1.2.3-59-g8ed1b