From nobody Fri Apr 3 06:28:34 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 743EE35CB69; Mon, 23 Feb 2026 10:45:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771843518; cv=none; b=eNXDbCroorsXeWDp22m/U5gdITg2qWMk63I3KU1hFkZMYf272VwHINb2Lv3OXG/fIi5Vbv1SluvG4XFBOAsCbI4J5w7L+KQaU4W0Cj3t137SuPEob1CRamnZdPO61IJFNBu9jxzPHVwHQ/CspSY1Ym9rO6XqkpKVrBLsLdic3O0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771843518; c=relaxed/simple; bh=oHaJZts+QrjYBNUL0bMFZBKLhJ1qXU7/bPzzxp7wO58=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=T1AWT3zfAaPOTfN5way2T5JJw6fVRE4ZDpf7RvrBJbSoxpk4rue92hcxJxEI8PP0Yp/XQNqNwgcS7Px1TopqfUEJZ/mJ2E0S69OhYf50dCxQWX16m+3iCGZvNrnhu52UPEoSoxD208ivTBMqhJ6fOWkUrKJi3cPTyiAI5K/Bvio= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LzIuw1Uc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LzIuw1Uc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29CC3C19424; Mon, 23 Feb 2026 10:45:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771843517; bh=oHaJZts+QrjYBNUL0bMFZBKLhJ1qXU7/bPzzxp7wO58=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=LzIuw1UcZqo8crcJGTUCNkCvgqnMYLPZ7bnAgR62mUKp6d2fEGPm8QGjzD6y7WnEJ 1LlDDRaGiPTF0ju0RcGeRqmh8/olqkkvgao9RnxmyOnnyL6WspVANjPJ+nKoajf7q5 U5ZZRGkyh9rFEFDaXyhnV5lz7ke816jxSrTn6/VcH3Pdq1yDsHpL+17gfi1+34Z3Vh +XbA9To/xpxiJ235ykFJb3q2X/AK4D5VG/coSOITLQiEig2s/T+oudt5K0WfRsqPoZ GJIxcGfLTF222H0K3FVmcU1UGfEvnLDi7huKveqAsHKQjTgaqPf5MgUvG21DTltdIZ 1Dj/h8COZatzg== From: Christian Brauner Date: Mon, 23 Feb 2026 11:44:58 +0100 Subject: [PATCH v4 1/4] clone: add CLONE_AUTOREAP Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260223-work-pidfs-autoreap-v4-1-e393c08c09d1@kernel.org> References: <20260223-work-pidfs-autoreap-v4-0-e393c08c09d1@kernel.org> In-Reply-To: <20260223-work-pidfs-autoreap-v4-0-e393c08c09d1@kernel.org> To: Oleg Nesterov , Jann Horn Cc: Linus Torvalds , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christian Brauner X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; a=openpgp-sha256; l=5721; i=brauner@kernel.org; h=from:subject:message-id; bh=oHaJZts+QrjYBNUL0bMFZBKLhJ1qXU7/bPzzxp7wO58=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWTO0d+pyTDF/M4U/mavb91T7RKyXodtXvaCaZHJB8sX7 ey6rSedOkpZGMS4GGTFFFkc2k3C5ZbzVGw2ytSAmcPKBDKEgYtTACZydyPDf7+0nun9t554XWEw 2P5XbFbJE82Xfos2XDdo2RjgWet0poKRYaN9BlPpI757D80+dS3P6LObYprXtrK554zmyn+PT4b 4cgAA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 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 =3D=3D 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 Signed-off-by: Christian Brauner --- include/linux/sched/signal.h | 1 + include/uapi/linux/sched.h | 1 + kernel/fork.c | 14 +++++++++++++- kernel/ptrace.c | 3 ++- kernel/signal.c | 4 ++++ 5 files changed, 21 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index a22248aebcf9..f842c86b806f 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -132,6 +132,7 @@ struct signal_struct { */ unsigned int is_child_subreaper:1; unsigned int has_child_subreaper:1; + unsigned int autoreap:1; =20 #ifdef CONFIG_POSIX_TIMERS =20 diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 359a14cc76a4..8a22ea640817 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -36,6 +36,7 @@ /* 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 g= iven the right permissions. */ +#define CLONE_AUTOREAP 0x400000000ULL /* Auto-reap child on exit. */ =20 /* * cloning flags intersect with CSIGNAL so can be used with unshare and cl= one3 diff --git a/kernel/fork.c b/kernel/fork.c index e832da9d15a4..0dedf2999f0c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2028,6 +2028,15 @@ __latent_entropy struct task_struct *copy_process( return ERR_PTR(-EINVAL); } =20 + if (clone_flags & CLONE_AUTOREAP) { + if (clone_flags & CLONE_THREAD) + return ERR_PTR(-EINVAL); + if (clone_flags & CLONE_PARENT) + return ERR_PTR(-EINVAL); + if (args->exit_signal) + return ERR_PTR(-EINVAL); + } + /* * Force any signals received before this point to be delivered * before the fork happens. Collect up signals sent to multiple @@ -2435,6 +2444,8 @@ __latent_entropy struct task_struct *copy_process( */ p->signal->has_child_subreaper =3D p->real_parent->signal->has_child_su= breaper || p->real_parent->signal->is_child_subreaper; + if (clone_flags & CLONE_AUTOREAP) + p->signal->autoreap =3D 1; list_add_tail(&p->sibling, &p->real_parent->children); list_add_tail_rcu(&p->tasks, &init_task.tasks); attach_pid(p, PIDTYPE_TGID); @@ -2897,7 +2908,8 @@ static bool clone3_args_valid(struct kernel_clone_arg= s *kargs) { /* Verify that no unknown flags are passed along. */ if (kargs->flags & - ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP)) + ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP | + CLONE_AUTOREAP)) return false; =20 /* diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 392ec2f75f01..68c17daef8d4 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -549,7 +549,8 @@ static bool __ptrace_detach(struct task_struct *tracer,= struct task_struct *p) if (!dead && thread_group_empty(p)) { if (!same_thread_group(p->real_parent, tracer)) dead =3D do_notify_parent(p, p->exit_signal); - else if (ignoring_children(tracer->sighand)) { + else if (ignoring_children(tracer->sighand) || + p->signal->autoreap) { __wake_up_parent(p, tracer); dead =3D true; } diff --git a/kernel/signal.c b/kernel/signal.c index d65d0fe24bfb..e61f39fa8c8a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2251,6 +2251,10 @@ bool do_notify_parent(struct task_struct *tsk, int s= ig) if (psig->action[SIGCHLD-1].sa.sa_handler =3D=3D SIG_IGN) sig =3D 0; } + if (!tsk->ptrace && tsk->signal->autoreap) { + autoreap =3D true; + sig =3D 0; + } /* * Send with __send_signal as si_pid and si_uid are in the * parent's namespaces. --=20 2.47.3