process-util: add new helper call for adjusting the OOM score

And let's make use of it in execute.c

src/basic/process-util.c

@@ -1445,6 +1445,15 @@ int fork_agent(const char *name, const int except[], size_t n_except, pid_t *ret
         _exit(EXIT_FAILURE);
 }
 
+int set_oom_score_adjust(int value) {
+        char t[DECIMAL_STR_MAX(int)];
+
+        sprintf(t, "%i", value);
+
+        return write_string_file("/proc/self/oom_score_adj", t,
+                                 WRITE_STRING_FILE_VERIFY_ON_FAILURE|WRITE_STRING_FILE_DISABLE_BUFFER);
+}
+
 static const char *const ioprio_class_table[] = {
         [IOPRIO_CLASS_NONE] = "none",
         [IOPRIO_CLASS_RT] = "realtime",

src/basic/process-util.h

@@ -173,6 +173,8 @@ static inline int safe_fork(const char *name, ForkFlags flags, pid_t *ret_pid) {
 
 int fork_agent(const char *name, const int except[], size_t n_except, pid_t *pid, const char *path, ...);
 
+int set_oom_score_adjust(int value);
+
 #if SIZEOF_PID_T == 4
 /* The highest possibly (theoretic) pid_t value on this architecture. */
 #define PID_T_MAX ((pid_t) INT32_MAX)

src/core/execute.c

@@ -2916,15 +2916,9 @@ static int exec_child(
         }
 
         if (context->oom_score_adjust_set) {
-                char t[DECIMAL_STR_MAX(context->oom_score_adjust)];
-
-                /* When we can't make this change due to EPERM, then
-                 * let's silently skip over it. User namespaces
-                 * prohibit write access to this file, and we
-                 * shouldn't trip up over that. */
-
-                sprintf(t, "%i", context->oom_score_adjust);
-                r = write_string_file("/proc/self/oom_score_adj", t, 0);
+                /* When we can't make this change due to EPERM, then let's silently skip over it. User namespaces
+                 * prohibit write access to this file, and we shouldn't trip up over that. */
+                r = set_oom_score_adjust(context->oom_score_adjust);
                 if (IN_SET(r, -EPERM, -EACCES))
                         log_unit_debug_errno(unit, r, "Failed to adjust OOM setting, assuming containerized execution, ignoring: %m");
                 else if (r < 0) {