shutdown: complain if process excluded from killing spree runs of the same rootfs as PID1

TODO

@@ -344,10 +344,6 @@ Features:
   - generate a failure of a default event loop is executed out-of-thread
   - maybe add support for inotify events
 
-* in the final killing spree, detect processes from the root directory, and
-  complain loudly if they have argv[0][0] == '@' set.
-  https://bugzilla.redhat.com/show_bug.cgi?id=961044
-
 * investigate endianness issues of UUID vs. GUID
 
 * dbus: when a unit failed to load (i.e. is in UNIT_ERROR state), we

src/basic/process-util.c

@@ -48,6 +48,7 @@
 #include "missing.h"
 #include "process-util.h"
 #include "signal-util.h"
+#include "stat-util.h"
 #include "string-table.h"
 #include "string-util.h"
 #include "user-util.h"
@@ -637,6 +638,17 @@ bool pid_is_alive(pid_t pid) {
         return true;
 }
 
+int pid_from_same_root_fs(pid_t pid) {
+        const char *root;
+
+        if (pid < 0)
+                return 0;
+
+        root = procfs_file_alloca(pid, "root");
+
+        return files_same(root, "/proc/1/root");
+}
+
 bool is_main_thread(void) {
         static thread_local int cached = 0;
 

src/basic/process-util.h

@@ -70,6 +70,7 @@ int getenv_for_pid(pid_t pid, const char *field, char **_value);
 
 bool pid_is_alive(pid_t pid);
 bool pid_is_unwaited(pid_t pid);
+int pid_from_same_root_fs(pid_t pid);
 
 bool is_main_thread(void);
 

src/core/killall.c

@@ -37,7 +37,7 @@
 
 #define TIMEOUT_USEC (10 * USEC_PER_SEC)
 
-static bool ignore_proc(pid_t pid) {
+static bool ignore_proc(pid_t pid, bool warn_rootfs) {
         _cleanup_fclose_ FILE *f = NULL;
         char c;
         const char *p;
@@ -72,7 +72,22 @@ static bool ignore_proc(pid_t pid) {
          * spree.
          *
          * http://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons */
-        if (count == 1 && c == '@')
+        if (c == '@' && warn_rootfs) {
+                _cleanup_free_ char *comm = NULL;
+
+                r = pid_from_same_root_fs(pid);
+                if (r < 0)
+                        return true;
+
+                get_process_comm(pid, &comm);
+
+                if (r)
+                        log_notice("Process " PID_FMT " (%s) has been been marked to be excluded from killing. It is "
+                                   "running from the root file system, and thus likely to block re-mounting of the "
+                                   "root file system to read-only. Please consider moving it into an initrd file "
+                                   "system instead.", pid, strna(comm));
+                return true;
+        } else if (c == '@')
                 return true;
 
         return false;
@@ -171,7 +186,7 @@ static int killall(int sig, Set *pids, bool send_sighup) {
                 if (parse_pid(d->d_name, &pid) < 0)
                         continue;
 
-                if (ignore_proc(pid))
+                if (ignore_proc(pid, sig == SIGKILL && !in_initrd()))
                         continue;
 
                 if (sig == SIGKILL) {