From 12ae2c81b21cfaa193db2faf035d495807edc3a7 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 26 Feb 2026 14:50:59 +0100 Subject: clone: add CLONE_AUTOREAP Add a new clone3() flag CLONE_AUTOREAP that makes a child process auto-reap on exit without ever becoming a zombie. This is a per-process property in contrast to the existing auto-reap mechanism via SA_NOCLDWAIT or SIG_IGN for SIGCHLD which applies to all children of a given parent. Currently the only way to automatically reap children is to set SA_NOCLDWAIT or SIG_IGN on SIGCHLD. This is a parent-scoped property affecting all children which makes it unsuitable for libraries or applications that need selective auto-reaping of specific children while still being able to wait() on others. CLONE_AUTOREAP stores an autoreap flag in the child's signal_struct. When the child exits do_notify_parent() checks this flag and causes exit_notify() to transition the task directly to EXIT_DEAD. Since the flag lives on the child it survives reparenting: if the original parent exits and the child is reparented to a subreaper or init the child still auto-reaps when it eventually exits. CLONE_AUTOREAP can be combined with CLONE_PIDFD to allow the parent to monitor the child's exit via poll() and retrieve exit status via PIDFD_GET_INFO. Without CLONE_PIDFD it provides a fire-and-forget pattern where the parent simply doesn't care about the child's exit status. No exit signal is delivered so exit_signal must be zero. CLONE_AUTOREAP is rejected in combination with CLONE_PARENT. If a CLONE_AUTOREAP child were to clone(CLONE_PARENT) the new grandchild would inherit exit_signal == 0 from the autoreap parent's group leader but without signal->autoreap. This grandchild would become a zombie that never sends a signal and is never autoreaped - confusing and arguably broken behavior. The flag is not inherited by the autoreap process's own children. Each child that should be autoreaped must be explicitly created with CLONE_AUTOREAP. Link: https://github.com/uapi-group/kernel-features/issues/45 Link: https://patch.msgid.link/20260226-work-pidfs-autoreap-v5-1-d148b984a989@kernel.org Reviewed-by: Oleg Nesterov Signed-off-by: Christian Brauner --- include/uapi/linux/sched.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/uapi') diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 359a14cc76a4..69f7b4f9eb0c 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -34,8 +34,9 @@ #define CLONE_IO 0x80000000 /* Clone io context */ /* Flags for the clone3() syscall. */ -#define CLONE_CLEAR_SIGHAND 0x100000000ULL /* Clear any signal handler and reset to SIG_DFL. */ -#define CLONE_INTO_CGROUP 0x200000000ULL /* Clone into a specific cgroup given the right permissions. */ +#define CLONE_CLEAR_SIGHAND (1ULL << 32) /* Clear any signal handler and reset to SIG_DFL. */ +#define CLONE_INTO_CGROUP (1ULL << 33) /* Clone into a specific cgroup given the right permissions. */ +#define CLONE_AUTOREAP (1ULL << 34) /* Auto-reap child on exit. */ /* * cloning flags intersect with CSIGNAL so can be used with unshare and clone3 -- cgit v1.2.3