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File _service:tar_scm:backport-scope-refuse-activation-of-scopes-if-no-PIDs-to-add-.patch of Package systemd (Revision 92b06b84c0445e4e6d1d412b716fdcc0)

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From 7ecb1b82d9b55a081d81b2802695fd21293ce029 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 27 Oct 2021 23:17:50 +0200
Subject: [PATCH] scope: refuse activation of scopes if no PIDs to add are left

If all processes we are supposed to add are gone by the time we are
ready to do so, let's fail.

THis is heavily based on Cunlong Li's work, who thankfully tracked this
down.

Replaces: #20577
(cherry picked from commit 8d3e4ac7cd37200d1431411a4b98925a24b7d9b3)

Conflict:NA
Reference:https://github.com/systemd/systemd/commit/7ecb1b82d9b55a081d81b2802695fd21293ce029
---
 src/core/cgroup.c | 3 ++-
 src/core/scope.c  | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index 1551d57e90..51936b7d1d 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -2196,7 +2196,8 @@ int unit_attach_pids_to_cgroup(Unit *u, Set *pids, const char *suffix_path) {
                                 ret = r; /* Remember first error */
 
                         continue;
-                }
+                } else if (ret >= 0)
+                        ret++; /* Count successful additions */
 
                 r = cg_all_unified();
                 if (r < 0)
diff --git a/src/core/scope.c b/src/core/scope.c
index af6311bb5f..fd4367dbed 100644
--- a/src/core/scope.c
+++ b/src/core/scope.c
@@ -374,6 +374,12 @@ static int scope_start(Unit *u) {
                 scope_enter_dead(s, SCOPE_FAILURE_RESOURCES);
                 return r;
         }
+        if (r == 0) {
+                log_unit_warning(u, "No PIDs left to attach to the scope's control group, refusing: %m");
+                scope_enter_dead(s, SCOPE_FAILURE_RESOURCES);
+                return -ECHILD;
+        }
+        log_unit_debug(u, "%i %s added to scope's control group.", r, r == 1 ? "process" : "processes");
 
         s->result = SCOPE_SUCCESS;
 
-- 
2.33.0