+/* Read the following fields from /proc/meminfo:
+ *
+ * NFS_Unstable
+ * Writeback
+ * Dirty
+ *
+ * Return true if the sum of these fields is greater than the previous
+ * value input. For all other issues, report the failure and indicate that
+ * the sync is not making progress.
+ */
+static bool sync_making_progress(unsigned long long *prev_dirty) {
+ _cleanup_fclose_ FILE *f = NULL;
+ char line[LINE_MAX];
+ bool r = false;
+ unsigned long long val = 0;
+
+ f = fopen("/proc/meminfo", "re");
+ if (!f)
+ return log_warning_errno(errno, "Failed to open /proc/meminfo: %m");
+
+ FOREACH_LINE(line, f, log_warning_errno(errno, "Failed to parse /proc/meminfo: %m")) {
+ unsigned long long ull = 0;
+
+ if (!first_word(line, "NFS_Unstable:") && !first_word(line, "Writeback:") && !first_word(line, "Dirty:"))
+ continue;
+
+ errno = 0;
+ if (sscanf(line, "%*s %llu %*s", &ull) != 1) {
+ if (errno != 0)
+ log_warning_errno(errno, "Failed to parse /proc/meminfo: %m");
+ else
+ log_warning("Failed to parse /proc/meminfo");
+
+ return false;
+ }
+
+ val += ull;
+ }
+
+ r = *prev_dirty > val;
+
+ *prev_dirty = val;
+
+ return r;
+}
+
+static void sync_with_progress(void) {
+ unsigned long long dirty = ULONG_LONG_MAX;
+ unsigned checks;
+ pid_t pid;
+ int r;
+
+ BLOCK_SIGNALS(SIGCHLD);
+
+ /* Due to the possiblity of the sync operation hanging, we fork a child process and monitor the progress. If
+ * the timeout lapses, the assumption is that that particular sync stalled. */
+
+ r = asynchronous_sync(&pid);
+ if (r < 0) {
+ log_error_errno(r, "Failed to fork sync(): %m");
+ return;
+ }
+
+ log_info("Syncing filesystems and block devices.");
+
+ /* Start monitoring the sync operation. If more than
+ * SYNC_PROGRESS_ATTEMPTS lapse without progress being made,
+ * we assume that the sync is stalled */
+ for (checks = 0; checks < SYNC_PROGRESS_ATTEMPTS; checks++) {
+ r = wait_for_terminate_with_timeout(pid, SYNC_TIMEOUT_USEC);
+ if (r == 0)
+ /* Sync finished without error.
+ * (The sync itself does not return an error code) */
+ return;
+ else if (r == -ETIMEDOUT) {
+ /* Reset the check counter if the "Dirty" value is
+ * decreasing */
+ if (sync_making_progress(&dirty))
+ checks = 0;
+ } else {
+ log_error_errno(r, "Failed to sync filesystems and block devices: %m");
+ return;
+ }
+ }
+
+ /* Only reached in the event of a timeout. We should issue a kill
+ * to the stray process. */
+ log_error("Syncing filesystems and block devices - timed out, issuing SIGKILL to PID "PID_FMT".", pid);
+ (void) kill(pid, SIGKILL);
+}
+