Merge pull request #6598 from kyle-walker/shutdown-limit

core: Limit the time and attempts in shutdown remount/umount efforts

src/basic/process-util.c

@@ -708,6 +708,67 @@ int wait_for_terminate_and_warn(const char *name, pid_t pid, bool check_exit_cod
         return -EPROTO;
 }
 
+/*
+ * Return values:
+ * < 0 : wait_for_terminate_with_timeout() failed to get the state of the
+ *       process, the process timed out, the process was terminated by a
+ *       signal, or failed for an unknown reason.
+ * >=0 : The process terminated normally with no failures.
+ *
+ * Success is indicated by a return value of zero, a timeout is indicated
+ * by ETIMEDOUT, and all other child failure states are indicated by error
+ * is indicated by a non-zero value.
+ */
+int wait_for_terminate_with_timeout(pid_t pid, usec_t timeout) {
+        sigset_t mask;
+        int r;
+        usec_t until;
+
+        assert_se(sigemptyset(&mask) == 0);
+        assert_se(sigaddset(&mask, SIGCHLD) == 0);
+
+        /* Drop into a sigtimewait-based timeout. Waiting for the
+         * pid to exit. */
+        until = now(CLOCK_MONOTONIC) + timeout;
+        for (;;) {
+                usec_t n;
+                siginfo_t status = {};
+                struct timespec ts;
+
+                n = now(CLOCK_MONOTONIC);
+                if (n >= until)
+                        break;
+
+                r = sigtimedwait(&mask, NULL, timespec_store(&ts, until - n)) < 0 ? -errno : 0;
+                /* Assuming we woke due to the child exiting. */
+                if (waitid(P_PID, pid, &status, WEXITED|WNOHANG) == 0) {
+                        if (status.si_pid == pid) {
+                                /* This is the correct child.*/
+                                if (status.si_code == CLD_EXITED)
+                                        return (status.si_status == 0) ? 0 : -EPROTO;
+                                else
+                                        return -EPROTO;
+                        }
+                }
+                /* Not the child, check for errors and proceed appropriately */
+                if (r < 0) {
+                        switch (r) {
+                        case -EAGAIN:
+                                /* Timed out, child is likely hung. */
+                                return -ETIMEDOUT;
+                        case -EINTR:
+                                /* Received a different signal and should retry */
+                                continue;
+                        default:
+                                /* Return any unexpected errors */
+                                return r;
+                        }
+                }
+        }
+
+        return -EPROTO;
+}
+
 void sigkill_wait(pid_t pid) {
         assert(pid > 1);