diff --git a/src/basic/calendarspec.c b/src/basic/calendarspec.c
index 6b3a9a4441..e6add0c383 100644
--- a/src/basic/calendarspec.c
+++ b/src/basic/calendarspec.c
@@ -24,6 +24,7 @@
 #include <limits.h>
 #include <stddef.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
@@ -261,19 +262,19 @@ static void format_weekdays(FILE *f, const CalendarSpec *c) {
 
                         if (l < 0) {
                                 if (need_comma)
-                                        fputc_unlocked(',', f);
+                                        fputc(',', f);
                                 else
                                         need_comma = true;
 
-                                fputs_unlocked(days[x], f);
+                                fputs(days[x], f);
                                 l = x;
                         }
 
                 } else if (l >= 0) {
 
                         if (x > l + 1) {
-                                fputs_unlocked(x > l + 2 ? ".." : ",", f);
-                                fputs_unlocked(days[x-1], f);
+                                fputs(x > l + 2 ? ".." : ",", f);
+                                fputs(days[x-1], f);
                         }
 
                         l = -1;
@@ -281,8 +282,8 @@ static void format_weekdays(FILE *f, const CalendarSpec *c) {
         }
 
         if (l >= 0 && x > l + 1) {
-                fputs_unlocked(x > l + 2 ? ".." : ",", f);
-                fputs_unlocked(days[x-1], f);
+                fputs(x > l + 2 ? ".." : ",", f);
+                fputs(days[x-1], f);
         }
 }
 
@@ -292,12 +293,12 @@ static void format_chain(FILE *f, int space, const CalendarComponent *c, bool us
         assert(f);
 
         if (!c) {
-                fputc_unlocked('*', f);
+                fputc('*', f);
                 return;
         }
 
         if (usec && c->start == 0 && c->repeat == USEC_PER_SEC && !c->next) {
-                fputc_unlocked('*', f);
+                fputc('*', f);
                 return;
         }
 
@@ -318,7 +319,7 @@ static void format_chain(FILE *f, int space, const CalendarComponent *c, bool us
                 fprintf(f, ".%06i", c->repeat % d);
 
         if (c->next) {
-                fputc_unlocked(',', f);
+                fputc(',', f);
                 format_chain(f, space, c->next, usec);
         }
 }
@@ -336,28 +337,30 @@ int calendar_spec_to_string(const CalendarSpec *c, char **p) {
         if (!f)
                 return -ENOMEM;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         if (c->weekdays_bits > 0 && c->weekdays_bits <= BITS_WEEKDAYS) {
                 format_weekdays(f, c);
-                fputc_unlocked(' ', f);
+                fputc(' ', f);
         }
 
         format_chain(f, 4, c->year, false);
-        fputc_unlocked('-', f);
+        fputc('-', f);
         format_chain(f, 2, c->month, false);
-        fputc_unlocked(c->end_of_month ? '~' : '-', f);
+        fputc(c->end_of_month ? '~' : '-', f);
         format_chain(f, 2, c->day, false);
-        fputc_unlocked(' ', f);
+        fputc(' ', f);
         format_chain(f, 2, c->hour, false);
-        fputc_unlocked(':', f);
+        fputc(':', f);
         format_chain(f, 2, c->minute, false);
-        fputc_unlocked(':', f);
+        fputc(':', f);
         format_chain(f, 2, c->microsecond, true);
 
         if (c->utc)
-                fputs_unlocked(" UTC", f);
+                fputs(" UTC", f);
         else if (c->timezone != NULL) {
-                fputc_unlocked(' ', f);
-                fputs_unlocked(c->timezone, f);
+                fputc(' ', f);
+                fputs(c->timezone, f);
         } else if (IN_SET(c->dst, 0, 1)) {
 
                 /* If daylight saving is explicitly on or off, let's show the used timezone. */
@@ -365,8 +368,8 @@ int calendar_spec_to_string(const CalendarSpec *c, char **p) {
                 tzset();
 
                 if (!isempty(tzname[c->dst])) {
-                        fputc_unlocked(' ', f);
-                        fputs_unlocked(tzname[c->dst], f);
+                        fputc(' ', f);
+                        fputs(tzname[c->dst], f);
                 }
         }
 
diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index 5774d4dea1..6dcd531025 100644
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -24,6 +24,7 @@
 #include <limits.h>
 #include <signal.h>
 #include <stddef.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
@@ -1032,6 +1033,8 @@ int cg_pid_get_path(const char *controller, pid_t pid, char **path) {
         if (!f)
                 return errno == ENOENT ? -ESRCH : -errno;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         FOREACH_LINE(line, f, return -errno) {
                 char *e, *p;
 
@@ -2371,6 +2374,8 @@ int cg_kernel_controllers(Set **ret) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         /* Ignore the header line */
         (void) read_line(f, (size_t) -1, NULL);
 
diff --git a/src/basic/fileio.c b/src/basic/fileio.c
index 3ab50bca2f..5296f1cff0 100644
--- a/src/basic/fileio.c
+++ b/src/basic/fileio.c
@@ -23,6 +23,7 @@
 #include <limits.h>
 #include <stdarg.h>
 #include <stdint.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
@@ -98,6 +99,7 @@ static int write_string_file_atomic(
         if (r < 0)
                 return r;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod_umask(fileno(f), 0644);
 
         r = write_string_stream_ts(f, line, flags, ts);
@@ -167,6 +169,8 @@ int write_string_file_ts(
                 }
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         if (flags & WRITE_STRING_FILE_DISABLE_BUFFER)
                 setvbuf(f, NULL, _IONBF, 0);
 
@@ -203,6 +207,8 @@ int read_one_line_file(const char *fn, char **line) {
         if (!f)
                 return -errno;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         r = read_line(f, LONG_LINE_MAX, line);
         return r < 0 ? r : 0;
 }
@@ -228,6 +234,8 @@ int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
         if (!f)
                 return -errno;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         /* We try to read one byte more than we need, so that we know whether we hit eof */
         errno = 0;
         k = fread(buf, 1, l + accept_extra_nl + 1, f);
@@ -323,6 +331,8 @@ int read_full_file(const char *fn, char **contents, size_t *size) {
         if (!f)
                 return -errno;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         return read_full_stream(f, contents, size);
 }
 
@@ -879,7 +889,8 @@ int write_env_file(const char *fname, char **l) {
         if (r < 0)
                 return r;
 
-        fchmod_umask(fileno(f), 0644);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod_umask(fileno(f), 0644);
 
         STRV_FOREACH(i, l)
                 write_env_var(f, *i);
diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c
index f8d615dd89..455c50fc9f 100644
--- a/src/basic/mount-util.c
+++ b/src/basic/mount-util.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <errno.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mount.h>
@@ -337,6 +338,8 @@ int umount_recursive(const char *prefix, int flags) {
                 if (!proc_self_mountinfo)
                         return -errno;
 
+                (void) __fsetlocking(proc_self_mountinfo, FSETLOCKING_BYCALLER);
+
                 for (;;) {
                         _cleanup_free_ char *path = NULL, *p = NULL;
                         int k;
@@ -583,6 +586,8 @@ int bind_remount_recursive(const char *prefix, bool ro, char **blacklist) {
         if (!proc_self_mountinfo)
                 return -errno;
 
+        (void) __fsetlocking(proc_self_mountinfo, FSETLOCKING_BYCALLER);
+
         return bind_remount_recursive_with_mountinfo(prefix, ro, blacklist, proc_self_mountinfo);
 }
 
diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 5f001494f0..32c3c951a1 100644
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -26,6 +26,7 @@
 #include <signal.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
@@ -130,6 +131,8 @@ int get_process_cmdline(pid_t pid, size_t max_length, bool comm_fallback, char *
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         if (max_length == 1) {
 
                 /* If there's only room for one byte, return the empty string */
@@ -406,6 +409,8 @@ int is_kernel_thread(pid_t pid) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         count = fread(&c, 1, 1, f);
         eof = feof(f);
         fclose(f);
@@ -487,6 +492,8 @@ static int get_process_id(pid_t pid, const char *field, uid_t *uid) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         FOREACH_LINE(line, f, return -errno) {
                 char *l;
 
@@ -565,6 +572,8 @@ int get_process_environ(pid_t pid, char **env) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         while ((c = fgetc(f)) != EOF) {
                 if (!GREEDY_REALLOC(outcome, allocated, sz + 5))
                         return -ENOMEM;
@@ -749,6 +758,8 @@ int getenv_for_pid(pid_t pid, const char *field, char **_value) {
                 return -errno;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         l = strlen(field);
         r = 0;
 
diff --git a/src/basic/string-util.c b/src/basic/string-util.c
index e916000b25..7e2f596edc 100644
--- a/src/basic/string-util.c
+++ b/src/basic/string-util.c
@@ -22,6 +22,7 @@
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -669,10 +670,10 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz) {
         if (!f)
                 return NULL;
 
-        /* Note we use the _unlocked() stdio variants on f for performance
-         * reasons.  It's safe to do so since we created f here and it
-         * doesn't leave our scope.
-         */
+        /* Note we turn off internal locking on f for performance reasons.  It's safe to do so since we created f here
+         * and it doesn't leave our scope. */
+
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 
         for (i = *ibuf; i < *ibuf + isz + 1; i++) {
 
@@ -684,21 +685,21 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz) {
                         else if (*i == '\x1B')
                                 state = STATE_ESCAPE;
                         else if (*i == '\t')
-                                fputs_unlocked("        ", f);
+                                fputs("        ", f);
                         else
-                                fputc_unlocked(*i, f);
+                                fputc(*i, f);
                         break;
 
                 case STATE_ESCAPE:
                         if (i >= *ibuf + isz) { /* EOT */
-                                fputc_unlocked('\x1B', f);
+                                fputc('\x1B', f);
                                 break;
                         } else if (*i == '[') {
                                 state = STATE_BRACKET;
                                 begin = i + 1;
                         } else {
-                                fputc_unlocked('\x1B', f);
-                                fputc_unlocked(*i, f);
+                                fputc('\x1B', f);
+                                fputc(*i, f);
                                 state = STATE_OTHER;
                         }
 
@@ -708,8 +709,8 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz) {
 
                         if (i >= *ibuf + isz || /* EOT */
                             (!(*i >= '0' && *i <= '9') && !IN_SET(*i, ';', 'm'))) {
-                                fputc_unlocked('\x1B', f);
-                                fputc_unlocked('[', f);
+                                fputc('\x1B', f);
+                                fputc('[', f);
                                 state = STATE_OTHER;
                                 i = begin-1;
                         } else if (*i == 'm')
diff --git a/src/busctl/busctl.c b/src/busctl/busctl.c
index 953816c46d..7547695e68 100644
--- a/src/busctl/busctl.c
+++ b/src/busctl/busctl.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <getopt.h>
+#include <stdio_ext.h>
 
 #include "sd-bus.h"
 
@@ -886,10 +887,8 @@ static int introspect(sd_bus *bus, char **argv) {
                 return log_oom();
 
         r = sd_bus_call_method(bus, argv[1], argv[2], "org.freedesktop.DBus.Introspectable", "Introspect", &error, &reply_xml, "");
-        if (r < 0) {
-                log_error("Failed to introspect object %s of service %s: %s", argv[2], argv[1], bus_error_message(&error, r));
-                return r;
-        }
+        if (r < 0)
+                return log_error_errno(r, "Failed to introspect object %s of service %s: %s", argv[2], argv[1], bus_error_message(&error, r));
 
         r = sd_bus_message_read(reply_xml, "s", &xml);
         if (r < 0)
@@ -914,10 +913,8 @@ static int introspect(sd_bus *bus, char **argv) {
                         continue;
 
                 r = sd_bus_call_method(bus, argv[1], argv[2], "org.freedesktop.DBus.Properties", "GetAll", &error, &reply, "s", m->interface);
-                if (r < 0) {
-                        log_error("%s", bus_error_message(&error, r));
-                        return r;
-                }
+                if (r < 0)
+                        return log_error_errno(r, "%s", bus_error_message(&error, r));
 
                 r = sd_bus_message_enter_container(reply, 'a', "{sv}");
                 if (r < 0)
@@ -949,22 +946,20 @@ static int introspect(sd_bus *bus, char **argv) {
                         if (!mf)
                                 return log_oom();
 
+                        (void) __fsetlocking(mf, FSETLOCKING_BYCALLER);
+
                         r = format_cmdline(reply, mf, false);
                         if (r < 0)
                                 return bus_log_parse_error(r);
 
-                        fclose(mf);
-                        mf = NULL;
+                        mf = safe_fclose(mf);
 
                         z = set_get(members, &((Member) {
                                                 .type = "property",
                                                 .interface = m->interface,
                                                 .name = (char*) name }));
-                        if (z) {
-                                free(z->value);
-                                z->value = buf;
-                                buf = NULL;
-                        }
+                        if (z)
+                                free_and_replace(z->value, buf);
 
                         r = sd_bus_message_exit_container(reply);
                         if (r < 0)
diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
index 690e3a3ca2..abca4e112d 100644
--- a/src/core/dbus-cgroup.c
+++ b/src/core/dbus-cgroup.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <arpa/inet.h>
+#include <stdio_ext.h>
 
 #include "af-list.h"
 #include "alloc-util.h"
@@ -687,6 +688,8 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
                         fprintf(f, "%s=\n", name);
                         LIST_FOREACH(device_limits, a, c->io_device_limits)
                                         if (a->limits[iol_type] != cgroup_io_limit_defaults[iol_type])
@@ -764,7 +767,9 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
-                        fputs_unlocked("IODeviceWeight=\n", f);
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+                        fputs("IODeviceWeight=\n", f);
                         LIST_FOREACH(device_weights, a, c->io_device_weights)
                                 fprintf(f, "IODeviceWeight=%s %" PRIu64 "\n", a->path, a->weight);
 
@@ -912,13 +917,15 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
                         if (read) {
-                                fputs_unlocked("BlockIOReadBandwidth=\n", f);
+                                fputs("BlockIOReadBandwidth=\n", f);
                                 LIST_FOREACH(device_bandwidths, a, c->blockio_device_bandwidths)
                                         if (a->rbps != CGROUP_LIMIT_MAX)
                                                 fprintf(f, "BlockIOReadBandwidth=%s %" PRIu64 "\n", a->path, a->rbps);
                         } else {
-                                fputs_unlocked("BlockIOWriteBandwidth=\n", f);
+                                fputs("BlockIOWriteBandwidth=\n", f);
                                 LIST_FOREACH(device_bandwidths, a, c->blockio_device_bandwidths)
                                         if (a->wbps != CGROUP_LIMIT_MAX)
                                                 fprintf(f, "BlockIOWriteBandwidth=%s %" PRIu64 "\n", a->path, a->wbps);
@@ -997,7 +1004,9 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
-                        fputs_unlocked("BlockIODeviceWeight=\n", f);
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+                        fputs("BlockIODeviceWeight=\n", f);
                         LIST_FOREACH(device_weights, a, c->blockio_device_weights)
                                 fprintf(f, "BlockIODeviceWeight=%s %" PRIu64 "\n", a->path, a->weight);
 
@@ -1229,7 +1238,9 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
-                        fputs_unlocked("DeviceAllow=\n", f);
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+                        fputs("DeviceAllow=\n", f);
                         LIST_FOREACH(device_allow, a, c->device_allow)
                                 fprintf(f, "DeviceAllow=%s %s%s%s\n", a->path, a->r ? "r" : "", a->w ? "w" : "", a->m ? "m" : "");
 
@@ -1399,8 +1410,10 @@ int bus_cgroup_set_property(
                         if (!f)
                                 return -ENOMEM;
 
-                        fputs_unlocked(name, f);
-                        fputs_unlocked("=\n", f);
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+                        fputs(name, f);
+                        fputs("=\n", f);
 
                         LIST_FOREACH(items, item, *list) {
                                 char buffer[CONST_MAX(INET_ADDRSTRLEN, INET6_ADDRSTRLEN)];
diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index 196de5658e..be25b6e987 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <sys/prctl.h>
+#include <stdio_ext.h>
 
 #if HAVE_SECCOMP
 #include <seccomp.h>
@@ -2202,6 +2203,8 @@ int bus_exec_context_set_transient_property(
                 if (!f)
                         return -ENOMEM;
 
+                (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
                 fputs("EnvironmentFile=\n", f);
 
                 STRV_FOREACH(i, c->environment_files) {
diff --git a/src/core/dbus-service.c b/src/core/dbus-service.c
index 8121765dad..0189952124 100644
--- a/src/core/dbus-service.c
+++ b/src/core/dbus-service.c
@@ -18,6 +18,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <stdio_ext.h>
+
 #include "alloc-util.h"
 #include "async.h"
 #include "bus-util.h"
@@ -313,7 +315,9 @@ static int bus_service_set_transient_property(
                         if (!f)
                                 return -ENOMEM;
 
-                        fputs_unlocked("ExecStart=\n", f);
+                        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+                        fputs("ExecStart=\n", f);
 
                         LIST_FOREACH(command, c, s->exec_command[ci]) {
                                 _cleanup_free_ char *a = NULL, *t = NULL;
diff --git a/src/core/manager.c b/src/core/manager.c
index 0681bbbbd2..7ac798348c 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -1754,7 +1754,7 @@ int manager_get_dump_string(Manager *m, char **ret) {
         if (!f)
                 return -errno;
 
-        __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 
         manager_dump(m, f, NULL);
 
@@ -2704,15 +2704,15 @@ int manager_serialize(Manager *m, FILE *f, FDSet *fds, bool switching_root) {
         manager_serialize_uid_refs(m, f);
         manager_serialize_gid_refs(m, f);
 
-        fputc_unlocked('\n', f);
+        (void) fputc('\n', f);
 
         HASHMAP_FOREACH_KEY(u, t, m->units, i) {
                 if (u->id != t)
                         continue;
 
                 /* Start marker */
-                fputs_unlocked(u->id, f);
-                fputc_unlocked('\n', f);
+                fputs(u->id, f);
+                fputc('\n', f);
 
                 r = unit_serialize(u, f, fds, !switching_root);
                 if (r < 0) {
diff --git a/src/core/smack-setup.c b/src/core/smack-setup.c
index a5b6ea2cd6..b0d3612d69 100644
--- a/src/core/smack-setup.c
+++ b/src/core/smack-setup.c
@@ -24,6 +24,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -243,20 +244,25 @@ static int write_netlabel_rules(const char* srcdir) {
                         continue;
                 }
 
+                (void) __fsetlocking(policy, FSETLOCKING_BYCALLER);
+
                 /* load2 write rules in the kernel require a line buffered stream */
                 FOREACH_LINE(buf, policy,
-                             log_error_errno(errno, "Failed to read line from %s: %m",
-                                       entry->d_name)) {
-                        if (!fputs_unlocked(buf, dst)) {
+                             log_error_errno(errno, "Failed to read line from %s: %m", entry->d_name)) {
+
+                        int q;
+
+                        if (!fputs(buf, dst)) {
                                 if (r == 0)
                                         r = -EINVAL;
                                 log_error_errno(errno, "Failed to write line to /sys/fs/smackfs/netlabel");
                                 break;
                         }
-                        if (fflush(dst)) {
+                        q = fflush_and_check(dst);
+                        if (q < 0) {
                                 if (r == 0)
-                                        r = -errno;
-                                log_error_errno(errno, "Failed to flush writes to /sys/fs/smackfs/netlabel: %m");
+                                        r = q;
+                                log_error_errno(q, "Failed to flush writes to /sys/fs/smackfs/netlabel: %m");
                                 break;
                         }
                 }
diff --git a/src/coredump/coredump.c b/src/coredump/coredump.c
index c7dd61f077..e6063cc980 100644
--- a/src/coredump/coredump.c
+++ b/src/coredump/coredump.c
@@ -20,6 +20,7 @@
 
 #include <errno.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <sys/prctl.h>
 #include <sys/xattr.h>
 #include <unistd.h>
@@ -540,6 +541,8 @@ static int compose_open_fds(pid_t pid, char **open_fds) {
         if (!stream)
                 return -ENOMEM;
 
+        (void) __fsetlocking(stream, FSETLOCKING_BYCALLER);
+
         FOREACH_DIRENT(dent, proc_fd_dir, return -errno) {
                 _cleanup_fclose_ FILE *fdinfo = NULL;
                 _cleanup_free_ char *fdname = NULL;
@@ -560,12 +563,12 @@ static int compose_open_fds(pid_t pid, char **open_fds) {
 
                 fdinfo = fdopen(fd, "re");
                 if (!fdinfo) {
-                        close(fd);
+                        safe_close(fd);
                         continue;
                 }
 
                 FOREACH_LINE(line, fdinfo, break) {
-                        fputs_unlocked(line, stream);
+                        fputs(line, stream);
                         if (!endswith(line, "\n"))
                                 fputc('\n', stream);
                 }
diff --git a/src/coredump/stacktrace.c b/src/coredump/stacktrace.c
index d37ffae020..95fd27b79a 100644
--- a/src/coredump/stacktrace.c
+++ b/src/coredump/stacktrace.c
@@ -20,6 +20,7 @@
 
 #include <dwarf.h>
 #include <elfutils/libdwfl.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "fd-util.h"
@@ -108,7 +109,7 @@ static int thread_callback(Dwfl_Thread *thread, void *userdata) {
                 return DWARF_CB_ABORT;
 
         if (c->n_thread != 0)
-                fputc_unlocked('\n', c->f);
+                fputc('\n', c->f);
 
         c->n_frame = 0;
 
@@ -145,6 +146,8 @@ int coredump_make_stack_trace(int fd, const char *executable, char **ret) {
         if (!c.f)
                 return -ENOMEM;
 
+        (void) __fsetlocking(c.f, FSETLOCKING_BYCALLER);
+
         elf_version(EV_CURRENT);
 
         c.elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
diff --git a/src/cryptsetup/cryptsetup-generator.c b/src/cryptsetup/cryptsetup-generator.c
index e2dc96bdb7..7e61332e52 100644
--- a/src/cryptsetup/cryptsetup-generator.c
+++ b/src/cryptsetup/cryptsetup-generator.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <errno.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "dropin.h"
@@ -117,6 +118,8 @@ static int create_disk(
         if (!f)
                 return log_error_errno(errno, "Failed to create unit file %s: %m", p);
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         fprintf(f,
                 "# Automatically generated by systemd-cryptsetup-generator\n\n"
                 "[Unit]\n"
@@ -136,7 +139,7 @@ static int create_disk(
 
         if (password) {
                 if (STR_IN_SET(password, "/dev/urandom", "/dev/random", "/dev/hw_random"))
-                        fputs_unlocked("After=systemd-random-seed.service\n", f);
+                        fputs("After=systemd-random-seed.service\n", f);
                 else if (!STR_IN_SET(password, "-", "none")) {
                         _cleanup_free_ char *uu;
 
@@ -168,8 +171,8 @@ static int create_disk(
                         d, d);
 
                 if (swap)
-                        fputs_unlocked("Before=dev-mapper-%i.swap\n",
-                                       f);
+                        fputs("Before=dev-mapper-%i.swap\n",
+                              f);
         } else
                 fprintf(f,
                         "RequiresMountsFor=%s\n",
@@ -372,6 +375,8 @@ static int add_crypttab_devices(void) {
                 return 0;
         }
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         if (fstat(fileno(f), &st) < 0) {
                 log_error_errno(errno, "Failed to stat /etc/crypttab: %m");
                 return 0;
diff --git a/src/fstab-generator/fstab-generator.c b/src/fstab-generator/fstab-generator.c
index c0886547e0..22c4ae9861 100644
--- a/src/fstab-generator/fstab-generator.c
+++ b/src/fstab-generator/fstab-generator.c
@@ -23,6 +23,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "fd-util.h"
@@ -134,11 +135,13 @@ static int add_swap(
                                        "Failed to create unit file %s: %m",
                                        unit);
 
-        fputs_unlocked("# Automatically generated by systemd-fstab-generator\n\n"
-                       "[Unit]\n"
-                       "SourcePath=/etc/fstab\n"
-                       "Documentation=man:fstab(5) man:systemd-fstab-generator(8)\n\n"
-                       "[Swap]\n", f);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+        fputs("# Automatically generated by systemd-fstab-generator\n\n"
+              "[Unit]\n"
+              "SourcePath=/etc/fstab\n"
+              "Documentation=man:fstab(5) man:systemd-fstab-generator(8)\n\n"
+              "[Swap]\n", f);
 
         r = write_what(f, what);
         if (r < 0)
@@ -370,6 +373,8 @@ static int add_mount(
                                        "Failed to create unit file %s: %m",
                                        unit);
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         fprintf(f,
                 "# Automatically generated by systemd-fstab-generator\n\n"
                 "[Unit]\n"
@@ -491,6 +496,8 @@ static int add_mount(
                 if (!f)
                         return log_error_errno(errno, "Failed to create unit file %s: %m", automount_unit);
 
+                (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
                 fprintf(f,
                         "# Automatically generated by systemd-fstab-generator\n\n"
                         "[Unit]\n"
diff --git a/src/journal/journal-qrcode.c b/src/journal/journal-qrcode.c
index 46ff1ce053..5a9dcaa525 100644
--- a/src/journal/journal-qrcode.c
+++ b/src/journal/journal-qrcode.c
@@ -22,6 +22,7 @@
 #include <qrencode.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 
 #include "journal-qrcode.h"
@@ -66,11 +67,13 @@ int print_qr_code(
         if (!f)
                 return -ENOMEM;
 
-        fputs_unlocked("fss://", f);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
+        fputs("fss://", f);
 
         for (i = 0; i < seed_size; i++) {
                 if (i > 0 && i % 3 == 0)
-                        fputc_unlocked('-', f);
+                        fputc('-', f);
                 fprintf(f, "%02x", ((uint8_t*) seed)[i]);
         }
 
diff --git a/src/libsystemd-network/sd-dhcp-lease.c b/src/libsystemd-network/sd-dhcp-lease.c
index a186bca38f..78b8e058b4 100644
--- a/src/libsystemd-network/sd-dhcp-lease.c
+++ b/src/libsystemd-network/sd-dhcp-lease.c
@@ -22,6 +22,7 @@
 #include <arpa/inet.h>
 #include <errno.h>
 #include <stdio.h>
+#include <stdio_ext.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -876,7 +877,8 @@ int dhcp_lease_save(sd_dhcp_lease *lease, const char *lease_file) {
         if (r < 0)
                 goto fail;
 
-        fchmod(fileno(f), 0644);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
                 "# This is private data. Do not parse.\n");
@@ -923,16 +925,16 @@ int dhcp_lease_save(sd_dhcp_lease *lease, const char *lease_file) {
 
         r = sd_dhcp_lease_get_dns(lease, &addresses);
         if (r > 0) {
-                fputs_unlocked("DNS=", f);
+                fputs("DNS=", f);
                 serialize_in_addrs(f, addresses, r);
-                fputs_unlocked("\n", f);
+                fputs("\n", f);
         }
 
         r = sd_dhcp_lease_get_ntp(lease, &addresses);
         if (r > 0) {
-                fputs_unlocked("NTP=", f);
+                fputs("NTP=", f);
                 serialize_in_addrs(f, addresses, r);
-                fputs_unlocked("\n", f);
+                fputs("\n", f);
         }
 
         r = sd_dhcp_lease_get_domainname(lease, &string);
@@ -941,9 +943,9 @@ int dhcp_lease_save(sd_dhcp_lease *lease, const char *lease_file) {
 
         r = sd_dhcp_lease_get_search_domains(lease, &search_domains);
         if (r > 0) {
-                fputs_unlocked("DOMAIN_SEARCH_LIST=", f);
+                fputs("DOMAIN_SEARCH_LIST=", f);
                 fputstrv(f, search_domains, NULL, NULL);
-                fputs_unlocked("\n", f);
+                fputs("\n", f);
         }
 
         r = sd_dhcp_lease_get_hostname(lease, &string);
diff --git a/src/libsystemd/sd-bus/bus-introspect.c b/src/libsystemd/sd-bus/bus-introspect.c
index 8a6e041748..9bd2dadfde 100644
--- a/src/libsystemd/sd-bus/bus-introspect.c
+++ b/src/libsystemd/sd-bus/bus-introspect.c
@@ -18,6 +18,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <stdio_ext.h>
+
 #include "bus-internal.h"
 #include "bus-introspect.h"
 #include "bus-protocol.h"
@@ -37,8 +39,10 @@ int introspect_begin(struct introspect *i, bool trusted) {
         if (!i->f)
                 return -ENOMEM;
 
-        fputs_unlocked(BUS_INTROSPECT_DOCTYPE
-                       "<node>\n", i->f);
+        (void) __fsetlocking(i->f, FSETLOCKING_BYCALLER);
+
+        fputs(BUS_INTROSPECT_DOCTYPE
+              "<node>\n", i->f);
 
         return 0;
 }
@@ -46,12 +50,12 @@ int introspect_begin(struct introspect *i, bool trusted) {
 int introspect_write_default_interfaces(struct introspect *i, bool object_manager) {
         assert(i);
 
-        fputs_unlocked(BUS_INTROSPECT_INTERFACE_PEER
-                       BUS_INTROSPECT_INTERFACE_INTROSPECTABLE
-                       BUS_INTROSPECT_INTERFACE_PROPERTIES, i->f);
+        fputs(BUS_INTROSPECT_INTERFACE_PEER
+              BUS_INTROSPECT_INTERFACE_INTROSPECTABLE
+              BUS_INTROSPECT_INTERFACE_PROPERTIES, i->f);
 
         if (object_manager)
-                fputs_unlocked(BUS_INTROSPECT_INTERFACE_OBJECT_MANAGER, i->f);
+                fputs(BUS_INTROSPECT_INTERFACE_OBJECT_MANAGER, i->f);
 
         return 0;
 }
@@ -77,27 +81,27 @@ int introspect_write_child_nodes(struct introspect *i, Set *s, const char *prefi
 
 static void introspect_write_flags(struct introspect *i, int type, int flags) {
         if (flags & SD_BUS_VTABLE_DEPRECATED)
-                fputs_unlocked("   <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
+                fputs("   <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
 
         if (type == _SD_BUS_VTABLE_METHOD && (flags & SD_BUS_VTABLE_METHOD_NO_REPLY))
-                fputs_unlocked("   <annotation name=\"org.freedesktop.DBus.Method.NoReply\" value=\"true\"/>\n", i->f);
+                fputs("   <annotation name=\"org.freedesktop.DBus.Method.NoReply\" value=\"true\"/>\n", i->f);
 
         if (IN_SET(type, _SD_BUS_VTABLE_PROPERTY, _SD_BUS_VTABLE_WRITABLE_PROPERTY)) {
                 if (flags & SD_BUS_VTABLE_PROPERTY_EXPLICIT)
-                        fputs_unlocked("   <annotation name=\"org.freedesktop.systemd1.Explicit\" value=\"true\"/>\n", i->f);
+                        fputs("   <annotation name=\"org.freedesktop.systemd1.Explicit\" value=\"true\"/>\n", i->f);
 
                 if (flags & SD_BUS_VTABLE_PROPERTY_CONST)
-                        fputs_unlocked("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"const\"/>\n", i->f);
+                        fputs("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"const\"/>\n", i->f);
                 else if (flags & SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION)
-                        fputs_unlocked("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"invalidates\"/>\n", i->f);
+                        fputs("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"invalidates\"/>\n", i->f);
                 else if (!(flags & SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE))
-                        fputs_unlocked("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"false\"/>\n", i->f);
+                        fputs("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"false\"/>\n", i->f);
         }
 
         if (!i->trusted &&
             IN_SET(type, _SD_BUS_VTABLE_METHOD, _SD_BUS_VTABLE_WRITABLE_PROPERTY) &&
             !(flags & SD_BUS_VTABLE_UNPRIVILEGED))
-                fputs_unlocked("   <annotation name=\"org.freedesktop.systemd1.Privileged\" value=\"true\"/>\n", i->f);
+                fputs("   <annotation name=\"org.freedesktop.systemd1.Privileged\" value=\"true\"/>\n", i->f);
 }
 
 static int introspect_write_arguments(struct introspect *i, const char *signature, const char *direction) {
@@ -118,7 +122,7 @@ static int introspect_write_arguments(struct introspect *i, const char *signatur
                 if (direction)
                         fprintf(i->f, " direction=\"%s\"/>\n", direction);
                 else
-                        fputs_unlocked("/>\n", i->f);
+                        fputs("/>\n", i->f);
 
                 signature += l;
         }
@@ -141,7 +145,7 @@ int introspect_write_interface(struct introspect *i, const sd_bus_vtable *v) {
 
                 case _SD_BUS_VTABLE_START:
                         if (v->flags & SD_BUS_VTABLE_DEPRECATED)
-                                fputs_unlocked("  <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
+                                fputs("  <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
                         break;
 
                 case _SD_BUS_VTABLE_METHOD:
@@ -149,7 +153,7 @@ int introspect_write_interface(struct introspect *i, const sd_bus_vtable *v) {
                         introspect_write_arguments(i, strempty(v->x.method.signature), "in");
                         introspect_write_arguments(i, strempty(v->x.method.result), "out");
                         introspect_write_flags(i, v->type, v->flags);
-                        fputs_unlocked("  </method>\n", i->f);
+                        fputs("  </method>\n", i->f);
                         break;
 
                 case _SD_BUS_VTABLE_PROPERTY:
@@ -159,14 +163,14 @@ int introspect_write_interface(struct introspect *i, const sd_bus_vtable *v) {
                                 v->x.property.signature,
                                 v->type == _SD_BUS_VTABLE_WRITABLE_PROPERTY ? "readwrite" : "read");
                         introspect_write_flags(i, v->type, v->flags);
-                        fputs_unlocked("  </property>\n", i->f);
+                        fputs("  </property>\n", i->f);
                         break;
 
                 case _SD_BUS_VTABLE_SIGNAL:
                         fprintf(i->f, "  <signal name=\"%s\">\n", v->x.signal.member);
                         introspect_write_arguments(i, strempty(v->x.signal.signature), NULL);
                         introspect_write_flags(i, v->type, v->flags);
-                        fputs_unlocked("  </signal>\n", i->f);
+                        fputs("  </signal>\n", i->f);
                         break;
                 }
 
@@ -183,7 +187,7 @@ int introspect_finish(struct introspect *i, sd_bus *bus, sd_bus_message *m, sd_b
         assert(m);
         assert(reply);
 
-        fputs_unlocked("</node>\n", i->f);
+        fputs("</node>\n", i->f);
 
         r = fflush_and_check(i->f);
         if (r < 0)
diff --git a/src/libsystemd/sd-bus/bus-match.c b/src/libsystemd/sd-bus/bus-match.c
index d5831a288c..8d798c0a58 100644
--- a/src/libsystemd/sd-bus/bus-match.c
+++ b/src/libsystemd/sd-bus/bus-match.c
@@ -18,6 +18,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <stdio_ext.h>
+
 #include "alloc-util.h"
 #include "bus-internal.h"
 #include "bus-match.h"
@@ -954,22 +956,24 @@ char *bus_match_to_string(struct bus_match_component *components, unsigned n_com
         if (!f)
                 return NULL;
 
+        __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         for (i = 0; i < n_components; i++) {
                 char buf[32];
 
                 if (i != 0)
-                        fputc_unlocked(',', f);
+                        fputc(',', f);
 
-                fputs_unlocked(bus_match_node_type_to_string(components[i].type, buf, sizeof(buf)), f);
-                fputc_unlocked('=', f);
-                fputc_unlocked('\'', f);
+                fputs(bus_match_node_type_to_string(components[i].type, buf, sizeof(buf)), f);
+                fputc('=', f);
+                fputc('\'', f);
 
                 if (components[i].type == BUS_MATCH_MESSAGE_TYPE)
-                        fputs_unlocked(bus_message_type_to_string(components[i].value_u8), f);
+                        fputs(bus_message_type_to_string(components[i].value_u8), f);
                 else
-                        fputs_unlocked(components[i].value_str, f);
+                        fputs(components[i].value_str, f);
 
-                fputc_unlocked('\'', f);
+                fputc('\'', f);
         }
 
         r = fflush_and_check(f);
diff --git a/src/libsystemd/sd-bus/bus-objects.c b/src/libsystemd/sd-bus/bus-objects.c
index 4c7dbaa2c9..121197bbcb 100644
--- a/src/libsystemd/sd-bus/bus-objects.c
+++ b/src/libsystemd/sd-bus/bus-objects.c
@@ -960,7 +960,7 @@ static int process_introspect(
                 if (!streq_ptr(previous_interface, c->interface)) {
 
                         if (previous_interface)
-                                fputs_unlocked(" </interface>\n", intro.f);
+                                fputs(" </interface>\n", intro.f);
 
                         fprintf(intro.f, " <interface name=\"%s\">\n", c->interface);
                 }
@@ -973,7 +973,7 @@ static int process_introspect(
         }
 
         if (previous_interface)
-                fputs_unlocked(" </interface>\n", intro.f);
+                fputs(" </interface>\n", intro.f);
 
         if (empty) {
                 /* Nothing?, let's see if we exist at all, and if not
diff --git a/src/locale/keymap-util.c b/src/locale/keymap-util.c
index 2457f8705c..2d788106bb 100644
--- a/src/locale/keymap-util.c
+++ b/src/locale/keymap-util.c
@@ -20,6 +20,7 @@
 ***/
 
 #include <errno.h>
+#include <stdio_ext.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -358,14 +359,15 @@ int x11_write_data(Context *c) {
         if (r < 0)
                 return r;
 
-        fchmod(fileno(f), 0644);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f), 0644);
 
-        fputs_unlocked("# Written by systemd-localed(8), read by systemd-localed and Xorg. It's\n"
-                       "# probably wise not to edit this file manually. Use localectl(1) to\n"
-                       "# instruct systemd-localed to update it.\n"
-                       "Section \"InputClass\"\n"
-                       "        Identifier \"system-keyboard\"\n"
-                       "        MatchIsKeyboard \"on\"\n", f);
+        fputs("# Written by systemd-localed(8), read by systemd-localed and Xorg. It's\n"
+              "# probably wise not to edit this file manually. Use localectl(1) to\n"
+              "# instruct systemd-localed to update it.\n"
+              "Section \"InputClass\"\n"
+              "        Identifier \"system-keyboard\"\n"
+              "        MatchIsKeyboard \"on\"\n", f);
 
         if (!isempty(c->x11_layout))
                 fprintf(f, "        Option \"XkbLayout\" \"%s\"\n", c->x11_layout);
@@ -379,7 +381,7 @@ int x11_write_data(Context *c) {
         if (!isempty(c->x11_options))
                 fprintf(f, "        Option \"XkbOptions\" \"%s\"\n", c->x11_options);
 
-        fputs_unlocked("EndSection\n", f);
+        fputs("EndSection\n", f);
 
         r = fflush_sync_and_check(f);
         if (r < 0)
diff --git a/src/login/logind-seat.c b/src/login/logind-seat.c
index f4aa9a6651..b99e7abf91 100644
--- a/src/login/logind-seat.c
+++ b/src/login/logind-seat.c
@@ -20,6 +20,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <stdio_ext.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -102,7 +103,8 @@ int seat_save(Seat *s) {
         if (r < 0)
                 goto fail;
 
-        fchmod(fileno(f), 0644);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
                 "# This is private data. Do not parse.\n"
@@ -128,7 +130,7 @@ int seat_save(Seat *s) {
         if (s->sessions) {
                 Session *i;
 
-                fputs_unlocked("SESSIONS=", f);
+                fputs("SESSIONS=", f);
                 LIST_FOREACH(sessions_by_seat, i, s->sessions) {
                         fprintf(f,
                                 "%s%c",
@@ -136,7 +138,7 @@ int seat_save(Seat *s) {
                                 i->sessions_by_seat_next ? ' ' : '\n');
                 }
 
-                fputs_unlocked("UIDS=", f);
+                fputs("UIDS=", f);
                 LIST_FOREACH(sessions_by_seat, i, s->sessions)
                         fprintf(f,
                                 UID_FMT"%c",
diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index 01469438b1..94e250b94a 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -22,6 +22,7 @@
 #include <string.h>
 #include <sys/mount.h>
 #include <unistd.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "bus-common-errors.h"
@@ -150,7 +151,8 @@ static int user_save_internal(User *u) {
         if (r < 0)
                 goto fail;
 
-        fchmod(fileno(f), 0644);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
                 "# This is private data. Do not parse.\n"
@@ -183,18 +185,18 @@ static int user_save_internal(User *u) {
                 Session *i;
                 bool first;
 
-                fputs_unlocked("SESSIONS=", f);
+                fputs("SESSIONS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->id, f);
+                        fputs(i->id, f);
                 }
 
-                fputs_unlocked("\nSEATS=", f);
+                fputs("\nSEATS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (!i->seat)
@@ -203,12 +205,12 @@ static int user_save_internal(User *u) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->seat->id, f);
+                        fputs(i->seat->id, f);
                 }
 
-                fputs_unlocked("\nACTIVE_SESSIONS=", f);
+                fputs("\nACTIVE_SESSIONS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (!session_is_active(i))
@@ -217,12 +219,12 @@ static int user_save_internal(User *u) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->id, f);
+                        fputs(i->id, f);
                 }
 
-                fputs_unlocked("\nONLINE_SESSIONS=", f);
+                fputs("\nONLINE_SESSIONS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (session_get_state(i) == SESSION_CLOSING)
@@ -231,12 +233,12 @@ static int user_save_internal(User *u) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->id, f);
+                        fputs(i->id, f);
                 }
 
-                fputs_unlocked("\nACTIVE_SEATS=", f);
+                fputs("\nACTIVE_SEATS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (!session_is_active(i) || !i->seat)
@@ -245,12 +247,12 @@ static int user_save_internal(User *u) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->seat->id, f);
+                        fputs(i->seat->id, f);
                 }
 
-                fputs_unlocked("\nONLINE_SEATS=", f);
+                fputs("\nONLINE_SEATS=", f);
                 first = true;
                 LIST_FOREACH(sessions_by_user, i, u->sessions) {
                         if (session_get_state(i) == SESSION_CLOSING || !i->seat)
@@ -259,11 +261,11 @@ static int user_save_internal(User *u) {
                         if (first)
                                 first = false;
                         else
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(i->seat->id, f);
+                        fputs(i->seat->id, f);
                 }
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         r = fflush_and_check(f);
diff --git a/src/machine/machine.c b/src/machine/machine.c
index 3d3c7cb6b8..0525c0cb03 100644
--- a/src/machine/machine.c
+++ b/src/machine/machine.c
@@ -21,6 +21,7 @@
 #include <errno.h>
 #include <string.h>
 #include <unistd.h>
+#include <stdio_ext.h>
 
 #include "sd-messages.h"
 
@@ -138,6 +139,7 @@ int machine_save(Machine *m) {
         if (r < 0)
                 goto fail;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
@@ -201,16 +203,16 @@ int machine_save(Machine *m) {
         if (m->n_netif > 0) {
                 unsigned i;
 
-                fputs_unlocked("NETIF=", f);
+                fputs("NETIF=", f);
 
                 for (i = 0; i < m->n_netif; i++) {
                         if (i != 0)
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
                         fprintf(f, "%i", m->netif[i]);
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         r = fflush_and_check(f);
diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index 6c4711e2e8..60ac980ad9 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -21,6 +21,7 @@
 #include <netinet/ether.h>
 #include <linux/if.h>
 #include <unistd.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "bus-util.h"
@@ -3360,16 +3361,16 @@ static void print_link_hashmap(FILE *f, const char *prefix, Hashmap* h) {
         if (hashmap_isempty(h))
                 return;
 
-        fputs_unlocked(prefix, f);
+        fputs(prefix, f);
         HASHMAP_FOREACH(link, h, i) {
                 if (space)
-                        fputc_unlocked(' ', f);
+                        fputc(' ', f);
 
                 fprintf(f, "%i", link->ifindex);
                 space = true;
         }
 
-        fputc_unlocked('\n', f);
+        fputc('\n', f);
 }
 
 int link_save(Link *link) {
@@ -3403,6 +3404,7 @@ int link_save(Link *link) {
         if (r < 0)
                 goto fail;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
@@ -3430,7 +3432,7 @@ int link_save(Link *link) {
 
                 fprintf(f, "NETWORK_FILE=%s\n", link->network->filename);
 
-                fputs_unlocked("DNS=", f);
+                fputs("DNS=", f);
                 space = false;
 
                 for (j = 0; j < link->network->n_dns; j++) {
@@ -3444,8 +3446,8 @@ int link_save(Link *link) {
                         }
 
                         if (space)
-                                fputc_unlocked(' ', f);
-                        fputs_unlocked(b, f);
+                                fputc(' ', f);
+                        fputs(b, f);
                         space = true;
                 }
 
@@ -3456,7 +3458,7 @@ int link_save(Link *link) {
                         r = sd_dhcp_lease_get_dns(link->dhcp_lease, &addresses);
                         if (r > 0) {
                                 if (space)
-                                        fputc_unlocked(' ', f);
+                                        fputc(' ', f);
                                 serialize_in_addrs(f, addresses, r);
                                 space = true;
                         }
@@ -3468,7 +3470,7 @@ int link_save(Link *link) {
                         r = sd_dhcp6_lease_get_dns(dhcp6_lease, &in6_addrs);
                         if (r > 0) {
                                 if (space)
-                                        fputc_unlocked(' ', f);
+                                        fputc(' ', f);
                                 serialize_in6_addrs(f, in6_addrs, r);
                                 space = true;
                         }
@@ -3482,16 +3484,16 @@ int link_save(Link *link) {
 
                         SET_FOREACH(dd, link->ndisc_rdnss, i) {
                                 if (space)
-                                        fputc_unlocked(' ', f);
+                                        fputc(' ', f);
 
                                 serialize_in6_addrs(f, &dd->address, 1);
                                 space = true;
                         }
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
 
-                fputs_unlocked("NTP=", f);
+                fputs("NTP=", f);
                 space = false;
                 fputstrv(f, link->network->ntp, NULL, &space);
 
@@ -3502,7 +3504,7 @@ int link_save(Link *link) {
                         r = sd_dhcp_lease_get_ntp(link->dhcp_lease, &addresses);
                         if (r > 0) {
                                 if (space)
-                                        fputc_unlocked(' ', f);
+                                        fputc(' ', f);
                                 serialize_in_addrs(f, addresses, r);
                                 space = true;
                         }
@@ -3516,7 +3518,7 @@ int link_save(Link *link) {
                                                          &in6_addrs);
                         if (r > 0) {
                                 if (space)
-                                        fputc_unlocked(' ', f);
+                                        fputc(' ', f);
                                 serialize_in6_addrs(f, in6_addrs, r);
                                 space = true;
                         }
@@ -3526,7 +3528,7 @@ int link_save(Link *link) {
                                 fputstrv(f, hosts, NULL, &space);
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
 
                 if (link->network->dhcp_use_domains != DHCP_USE_DOMAINS_NO) {
                         if (link->dhcp_lease) {
@@ -3537,7 +3539,7 @@ int link_save(Link *link) {
                                 (void) sd_dhcp6_lease_get_domains(dhcp6_lease, &dhcp6_domains);
                 }
 
-                fputs_unlocked("DOMAINS=", f);
+                fputs("DOMAINS=", f);
                 space = false;
                 fputstrv(f, link->network->search_domains, NULL, &space);
 
@@ -3555,9 +3557,9 @@ int link_save(Link *link) {
                                 fputs_with_space(f, NDISC_DNSSL_DOMAIN(dd), NULL, &space);
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
 
-                fputs_unlocked("ROUTE_DOMAINS=", f);
+                fputs("ROUTE_DOMAINS=", f);
                 space = false;
                 fputstrv(f, link->network->route_domains, NULL, &space);
 
@@ -3575,7 +3577,7 @@ int link_save(Link *link) {
                                 fputs_with_space(f, NDISC_DNSSL_DOMAIN(dd), NULL, &space);
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
 
                 fprintf(f, "LLMNR=%s\n",
                         resolve_support_to_string(link->network->llmnr));
@@ -3589,14 +3591,14 @@ int link_save(Link *link) {
                 if (!set_isempty(link->network->dnssec_negative_trust_anchors)) {
                         const char *n;
 
-                        fputs_unlocked("DNSSEC_NTA=", f);
+                        fputs("DNSSEC_NTA=", f);
                         space = false;
                         SET_FOREACH(n, link->network->dnssec_negative_trust_anchors, i)
                                 fputs_with_space(f, n, NULL, &space);
-                        fputc_unlocked('\n', f);
+                        fputc('\n', f);
                 }
 
-                fputs_unlocked("ADDRESSES=", f);
+                fputs("ADDRESSES=", f);
                 space = false;
                 SET_FOREACH(a, link->addresses, i) {
                         _cleanup_free_ char *address_str = NULL;
@@ -3608,9 +3610,9 @@ int link_save(Link *link) {
                         fprintf(f, "%s%s/%u", space ? " " : "", address_str, a->prefixlen);
                         space = true;
                 }
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
 
-                fputs_unlocked("ROUTES=", f);
+                fputs("ROUTES=", f);
                 space = false;
                 SET_FOREACH(route, link->routes, i) {
                         _cleanup_free_ char *route_str = NULL;
@@ -3625,7 +3627,7 @@ int link_save(Link *link) {
                         space = true;
                 }
 
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         print_link_hashmap(f, "CARRIER_BOUND_TO=", link->bound_to_links);
@@ -3643,9 +3645,9 @@ int link_save(Link *link) {
 
                 r = sd_dhcp_lease_get_address(link->dhcp_lease, &address);
                 if (r >= 0) {
-                        fputs_unlocked("DHCP4_ADDRESS=", f);
+                        fputs("DHCP4_ADDRESS=", f);
                         serialize_in_addrs(f, &address, 1);
-                        fputc_unlocked('\n', f);
+                        fputc('\n', f);
                 }
 
                 r = dhcp_lease_save(link->dhcp_lease, link->lease_file);
@@ -3663,9 +3665,9 @@ int link_save(Link *link) {
 
                 r = sd_ipv4ll_get_address(link->ipv4ll, &address);
                 if (r >= 0) {
-                        fputs_unlocked("IPV4LL_ADDRESS=", f);
+                        fputs("IPV4LL_ADDRESS=", f);
                         serialize_in_addrs(f, &address, 1);
-                        fputc_unlocked('\n', f);
+                        fputc('\n', f);
                 }
         }
 
diff --git a/src/network/networkd-manager.c b/src/network/networkd-manager.c
index c2c41d978b..cc17af9391 100644
--- a/src/network/networkd-manager.c
+++ b/src/network/networkd-manager.c
@@ -21,6 +21,7 @@
 #include <sys/socket.h>
 #include <linux/if.h>
 #include <linux/fib_rules.h>
+#include <stdio_ext.h>
 
 #include "sd-daemon.h"
 #include "sd-netlink.h"
@@ -991,12 +992,12 @@ static void print_string_set(FILE *f, const char *field, OrderedSet *s) {
         if (ordered_set_isempty(s))
                 return;
 
-        fputs_unlocked(field, f);
+        fputs(field, f);
 
         ORDERED_SET_FOREACH(p, s, i)
                 fputs_with_space(f, p, NULL, &space);
 
-        fputc_unlocked('\n', f);
+        fputc('\n', f);
 }
 
 static int manager_save(Manager *m) {
@@ -1114,6 +1115,7 @@ static int manager_save(Manager *m) {
         if (r < 0)
                 return r;
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
         (void) fchmod(fileno(f), 0644);
 
         fprintf(f,
diff --git a/src/resolve/resolved-link.c b/src/resolve/resolved-link.c
index ed7bdc848a..e3e50eca53 100644
--- a/src/resolve/resolved-link.c
+++ b/src/resolve/resolved-link.c
@@ -19,6 +19,7 @@
 ***/
 
 #include <net/if.h>
+#include <stdio_ext.h>
 
 #include "sd-network.h"
 
@@ -1100,7 +1101,10 @@ int link_save_user(Link *l) {
         if (r < 0)
                 goto fail;
 
-        fputs_unlocked("# This is private data. Do not parse.\n", f);
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f), 0644);
+
+        fputs("# This is private data. Do not parse.\n", f);
 
         v = resolve_support_to_string(l->llmnr_support);
         if (v)
@@ -1117,11 +1121,11 @@ int link_save_user(Link *l) {
         if (l->dns_servers) {
                 DnsServer *server;
 
-                fputs_unlocked("SERVERS=", f);
+                fputs("SERVERS=", f);
                 LIST_FOREACH(servers, server, l->dns_servers) {
 
                         if (server != l->dns_servers)
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
                         v = dns_server_string(server);
                         if (!v) {
@@ -1129,26 +1133,26 @@ int link_save_user(Link *l) {
                                 goto fail;
                         }
 
-                        fputs_unlocked(v, f);
+                        fputs(v, f);
                 }
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         if (l->search_domains) {
                 DnsSearchDomain *domain;
 
-                fputs_unlocked("DOMAINS=", f);
+                fputs("DOMAINS=", f);
                 LIST_FOREACH(domains, domain, l->search_domains) {
 
                         if (domain != l->search_domains)
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
                         if (domain->route_only)
-                                fputc_unlocked('~', f);
+                                fputc('~', f);
 
-                        fputs_unlocked(DNS_SEARCH_DOMAIN_NAME(domain), f);
+                        fputs(DNS_SEARCH_DOMAIN_NAME(domain), f);
                 }
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         if (!set_isempty(l->dnssec_negative_trust_anchors)) {
@@ -1156,16 +1160,16 @@ int link_save_user(Link *l) {
                 Iterator i;
                 char *nta;
 
-                fputs_unlocked("NTAS=", f);
+                fputs("NTAS=", f);
                 SET_FOREACH(nta, l->dnssec_negative_trust_anchors, i) {
 
                         if (space)
-                                fputc_unlocked(' ', f);
+                                fputc(' ', f);
 
-                        fputs_unlocked(nta, f);
+                        fputs(nta, f);
                         space = true;
                 }
-                fputc_unlocked('\n', f);
+                fputc('\n', f);
         }
 
         r = fflush_and_check(f);
diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index 983e6c091a..2dbf432df9 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -20,6 +20,7 @@
 
 #include <netinet/in.h>
 #include <poll.h>
+#include <stdio_ext.h>
 #include <sys/ioctl.h>
 
 #if HAVE_LIBIDN2
@@ -535,6 +536,8 @@ static int manager_sigusr1(sd_event_source *s, const struct signalfd_siginfo *si
         if (!f)
                 return log_oom();
 
+        (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
+
         LIST_FOREACH(scopes, scope, m->dns_scopes)
                 dns_scope_dump(scope, f);
 
diff --git a/src/resolve/resolved-resolv-conf.c b/src/resolve/resolved-resolv-conf.c
index 4ea7490ac9..bad04d6a29 100644
--- a/src/resolve/resolved-resolv-conf.c
+++ b/src/resolve/resolved-resolv-conf.c
@@ -19,6 +19,7 @@
  ***/
 
 #include <resolv.h>
+#include <stdio_ext.h>
 
 #include "alloc-util.h"
 #include "dns-domain.h"
@@ -201,7 +202,7 @@ static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
         }
 
         if (*count == MAXNS)
-                fputs_unlocked("# Too many DNS servers configured, the following entries may be ignored.\n", f);
+                fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
         (*count)++;
 
         fprintf(f, "nameserver %s\n", dns_server_string(s));
@@ -217,43 +218,43 @@ static void write_resolv_conf_search(
         assert(domains);
         assert(f);
 
-        fputs_unlocked("search", f);
+        fputs("search", f);
 
         ORDERED_SET_FOREACH(domain, domains, i) {
                 if (++count > MAXDNSRCH) {
-                        fputs_unlocked("\n# Too many search domains configured, remaining ones ignored.", f);
+                        fputs("\n# Too many search domains configured, remaining ones ignored.", f);
                         break;
                 }
                 length += strlen(domain) + 1;
                 if (length > 256) {
-                        fputs_unlocked("\n# Total length of all search domains is too long, remaining ones ignored.", f);
+                        fputs("\n# Total length of all search domains is too long, remaining ones ignored.", f);
                         break;
                 }
-                fputc_unlocked(' ', f);
-                fputs_unlocked(domain, f);
+                fputc(' ', f);
+                fputs(domain, f);
         }
 
-        fputs_unlocked("\n", f);
+        fputs("\n", f);
 }
 
 static int write_uplink_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
         Iterator i;
 
-        fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
-                       "#\n"
-                       "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
-                       "# all known uplink DNS servers. This file lists all configured search domains.\n"
-                       "#\n"
-                       "# Third party programs must not access this file directly, but only through the\n"
-                       "# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
-                       "# replace this symlink by a static file or a different symlink.\n"
-                       "#\n"
-                       "# See man:systemd-resolved.service(8) for details about the supported modes of\n"
-                       "# operation for /etc/resolv.conf.\n"
-                       "\n", f);
+        fputs("# This file is managed by man:systemd-resolved(8). Do not edit.\n"
+              "#\n"
+              "# This is a dynamic resolv.conf file for connecting local clients directly to\n"
+              "# all known uplink DNS servers. This file lists all configured search domains.\n"
+              "#\n"
+              "# Third party programs must not access this file directly, but only through the\n"
+              "# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
+              "# replace this symlink by a static file or a different symlink.\n"
+              "#\n"
+              "# See man:systemd-resolved.service(8) for details about the supported modes of\n"
+              "# operation for /etc/resolv.conf.\n"
+              "\n", f);
 
         if (ordered_set_isempty(dns))
-                fputs_unlocked("# No DNS servers known.\n", f);
+                fputs("# No DNS servers known.\n", f);
         else {
                 unsigned count = 0;
                 DnsServer *s;
@@ -296,10 +297,8 @@ static int write_stub_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet
 int manager_write_resolv_conf(Manager *m) {
 
         _cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
-        _cleanup_free_ char *temp_path_uplink = NULL;
-        _cleanup_free_ char *temp_path_stub = NULL;
-        _cleanup_fclose_ FILE *f_uplink = NULL;
-        _cleanup_fclose_ FILE *f_stub = NULL;
+        _cleanup_free_ char *temp_path_uplink = NULL, *temp_path_stub = NULL;
+        _cleanup_fclose_ FILE *f_uplink = NULL, *f_stub = NULL;
         int r;
 
         assert(m);
@@ -319,10 +318,15 @@ int manager_write_resolv_conf(Manager *m) {
         r = fopen_temporary_label(PRIVATE_UPLINK_RESOLV_CONF, PRIVATE_UPLINK_RESOLV_CONF, &f_uplink, &temp_path_uplink);
         if (r < 0)
                 return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
+
+        (void) __fsetlocking(f_uplink, FSETLOCKING_BYCALLER);
+        (void) fchmod(fileno(f_uplink), 0644);
+
         r = fopen_temporary_label(PRIVATE_STUB_RESOLV_CONF, PRIVATE_STUB_RESOLV_CONF, &f_stub, &temp_path_stub);
         if (r < 0)
                 return log_warning_errno(r, "Failed to open private stub-resolv.conf file for writing: %m");
-        (void) fchmod(fileno(f_uplink), 0644);
+
+        (void) __fsetlocking(f_stub, FSETLOCKING_BYCALLER);
         (void) fchmod(fileno(f_stub), 0644);
 
         r = write_uplink_resolv_conf_contents(f_uplink, dns, domains);