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From f057aa6bb604845fa10ad569bca306e5e1e8fe0d Mon Sep 17 00:00:00 2001
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From: Franck Bui <fbui@suse.com>
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Date: Mon, 18 Mar 2019 11:48:34 +0100
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Subject: [PATCH] process-util: introduce pid_is_my_child() helper
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No functional changes.
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Thanks Renaud Métrich for backporting this to RHEL.
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Resolves: #1744972
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---
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 src/basic/process-util.c | 14 ++++++++++++++
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 src/basic/process-util.h |  1 +
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 src/core/cgroup.c        |  7 ++-----
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 src/core/service.c       |  8 ++------
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 4 files changed, 19 insertions(+), 11 deletions(-)
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diff --git a/src/basic/process-util.c b/src/basic/process-util.c
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index aa3eff779a..6dbeee9dda 100644
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--- a/src/basic/process-util.c
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+++ b/src/basic/process-util.c
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@@ -903,6 +903,20 @@ int getenv_for_pid(pid_t pid, const char *field, char **ret) {
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         return 0;
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 }
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+int pid_is_my_child(pid_t pid) {
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+        pid_t ppid;
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+        int r;
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+
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+        if (pid <= 1)
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+                return false;
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+
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+        r = get_process_ppid(pid, &ppid);
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+        if (r < 0)
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+                return r;
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+
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+        return ppid == getpid_cached();
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+}
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+
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 bool pid_is_unwaited(pid_t pid) {
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         /* Checks whether a PID is still valid at all, including a zombie */
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diff --git a/src/basic/process-util.h b/src/basic/process-util.h
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index a5bb072b25..a3bd2851b4 100644
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--- a/src/basic/process-util.h
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+++ b/src/basic/process-util.h
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@@ -68,6 +68,7 @@ int getenv_for_pid(pid_t pid, const char *field, char **_value);
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 bool pid_is_alive(pid_t pid);
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 bool pid_is_unwaited(pid_t pid);
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+int pid_is_my_child(pid_t pid);
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 int pid_from_same_root_fs(pid_t pid);
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 bool is_main_thread(void);
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diff --git a/src/core/cgroup.c b/src/core/cgroup.c
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index 62ab41a288..b7ed07e65b 100644
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--- a/src/core/cgroup.c
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+++ b/src/core/cgroup.c
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@@ -1876,7 +1876,7 @@ void unit_prune_cgroup(Unit *u) {
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 int unit_search_main_pid(Unit *u, pid_t *ret) {
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         _cleanup_fclose_ FILE *f = NULL;
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-        pid_t pid = 0, npid, mypid;
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+        pid_t pid = 0, npid;
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         int r;
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         assert(u);
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@@ -1889,15 +1889,12 @@ int unit_search_main_pid(Unit *u, pid_t *ret) {
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         if (r < 0)
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                 return r;
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-        mypid = getpid_cached();
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         while (cg_read_pid(f, &npid) > 0)  {
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-                pid_t ppid;
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                 if (npid == pid)
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                         continue;
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-                /* Ignore processes that aren't our kids */
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-                if (get_process_ppid(npid, &ppid) >= 0 && ppid != mypid)
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+                if (pid_is_my_child(npid) == 0)
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                         continue;
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                 if (pid != 0)
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diff --git a/src/core/service.c b/src/core/service.c
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index 24f167572a..614ba05d89 100644
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--- a/src/core/service.c
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+++ b/src/core/service.c
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@@ -139,8 +139,6 @@ static void service_unwatch_pid_file(Service *s) {
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 }
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 static int service_set_main_pid(Service *s, pid_t pid) {
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-        pid_t ppid;
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-
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         assert(s);
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         if (pid <= 1)
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@@ -159,12 +157,10 @@ static int service_set_main_pid(Service *s, pid_t pid) {
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         s->main_pid = pid;
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         s->main_pid_known = true;
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+        s->main_pid_alien = pid_is_my_child(pid) == 0;
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-        if (get_process_ppid(pid, &ppid) >= 0 && ppid != getpid_cached()) {
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+        if (s->main_pid_alien)
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                 log_unit_warning(UNIT(s), "Supervising process "PID_FMT" which is not our child. We'll most likely not notice when it exits.", pid);
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-                s->main_pid_alien = true;
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-        } else
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-                s->main_pid_alien = false;
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         return 0;
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 }