From 07612aab66dc771a9c7aca07c74940fb6447f3fa Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Wed, 20 Nov 2024 15:12:25 +0100
Subject: [PATCH 1/2] process-util: use our usual tristate semantics for
 is_main_thread()

While at it, _unlikely_ is dropped, as requested in
https://github.com/systemd/systemd/pull/35242#discussion_r1880096233
---
 src/basic/process-util.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 3253a9c3fb..59dfaa07f3 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -1226,12 +1226,12 @@ int pid_from_same_root_fs(pid_t pid) {
 }
 
 bool is_main_thread(void) {
-        static thread_local int cached = 0;
+        static thread_local int cached = -1;
 
-        if (_unlikely_(cached == 0))
-                cached = getpid_cached() == gettid() ? 1 : -1;
+        if (cached < 0)
+                cached = getpid_cached() == gettid();
 
-        return cached > 0;
+        return cached;
 }
 
 bool oom_score_adjust_is_valid(int oa) {

From 61263e143634db1eab916fa119f70ca15c1043db Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Thu, 28 Nov 2024 00:40:11 +0100
Subject: [PATCH 2/2] process-util: make sure we don't report ppid == 0

Previously, if pid == 0 and we're PID 1, get_process_ppid()
would set ret to getppid(), i.e. 0, which is inconsistent
when pid is explicitly set to 1. Ensure we always handle
such case by returning -EADDRNOTAVAIL.
---
 src/basic/process-util.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 59dfaa07f3..c74a7e7ea4 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -702,15 +702,17 @@ int get_process_ppid(pid_t pid, pid_t *ret) {
 
         assert(pid >= 0);
 
-        if (pid == 0 || pid == getpid_cached()) {
+        if (pid == 0)
+                pid = getpid_cached();
+        if (pid == 1) /* PID 1 has no parent, shortcut this case */
+                return -EADDRNOTAVAIL;
+
+        if (pid == getpid_cached()) {
                 if (ret)
                         *ret = getppid();
                 return 0;
         }
 
-        if (pid == 1) /* PID 1 has no parent, shortcut this case */
-                return -EADDRNOTAVAIL;
-
         p = procfs_file_alloca(pid, "stat");
         r = read_one_line_file(p, &line);
         if (r == -ENOENT)
@@ -724,7 +726,6 @@ int get_process_ppid(pid_t pid, pid_t *ret) {
         p = strrchr(line, ')');
         if (!p)
                 return -EIO;
-
         p++;
 
         if (sscanf(p, " "
@@ -733,9 +734,9 @@ int get_process_ppid(pid_t pid, pid_t *ret) {
                    &ppid) != 1)
                 return -EIO;
 
-        /* If ppid is zero the process has no parent. Which might be the case for PID 1 but also for
-         * processes originating in other namespaces that are inserted into a pidns. Return a recognizable
-         * error in this case. */
+        /* If ppid is zero the process has no parent. Which might be the case for PID 1 (caught above)
+         * but also for processes originating in other namespaces that are inserted into a pidns.
+         * Return a recognizable error in this case. */
         if (ppid == 0)
                 return -EADDRNOTAVAIL;