sched: Only setting CPUSchedulingPriority=rr doesn't work

A service that only sets the scheduling policy to round-robin
fails to be started. This is because the cpu_sched_priority is
initialized to 0 and is not adjusted when the policy is changed.

Clamp the cpu_sched_priority when the scheduler policy is set. Use
the current policy to validate the new priority.

Change the manual page to state that the given range only applies
to the real-time scheduling policies.

Add a testcase that verifies this change:

$ make test-sched-prio; ./test-sched-prio
[test/sched_idle_bad.service:6] CPU scheduling priority is out of range, ignoring: 1
[test/sched_rr_bad.service:7] CPU scheduling priority is out of range, ignoring: 0
[test/sched_rr_bad.service:8] CPU scheduling priority is out of range, ignoring: 100

.gitignore

@@ -90,6 +90,7 @@
 /systemd
 /test-engine
 /test-job-type
+/test-sched-prio
 /systemctl
 /systemadm
 .dirstamp

Makefile.am

@@ -1185,7 +1185,8 @@ noinst_PROGRAMS += \
 	test-unit-file \
 	test-date \
 	test-sleep \
-	test-replace-var
+	test-replace-var \
+	test-sched-prio
 
 TESTS += \
 	test-job-type \
@@ -1195,7 +1196,15 @@ TESTS += \
 	test-unit-file \
 	test-date \
 	test-sleep \
-	test-replace-var
+	test-replace-var \
+	test-sched-prio
+
+EXTRA_DIST += \
+	test/sched_idle_bad.service \
+	test/sched_idle_ok.service \
+	test/sched_rr_bad.service \
+	test/sched_rr_ok.service \
+	test/sched_rr_change.service
 
 test_engine_SOURCES = \
 	src/test/test-engine.c
@@ -1323,6 +1332,18 @@ test_watchdog_SOURCES = \
 test_watchdog_LDADD = \
 	libsystemd-shared.la
 
+test_sched_prio_SOURCES = \
+	src/test/test-sched-prio.c
+
+test_sched_prio_CFLAGS = \
+	$(AM_CFLAGS) \
+	$(DBUS_CFLAGS) \
+	-D"STR(s)=\#s" -D"TEST_DIR=STR($(abs_top_srcdir)/test/)"
+
+test_sched_prio_LDADD = \
+	libsystemd-core.la \
+	libsystemd-daemon.la
+
 # ------------------------------------------------------------------------------
 systemd_initctl_SOURCES = \
 	src/initctl/initctl.c

man/systemd.exec.xml

@@ -214,13 +214,15 @@
 
                                 <listitem><para>Sets the CPU
                                 scheduling priority for executed
-                                processes. Takes an integer between 1
-                                (lowest priority) and 99 (highest
-                                priority). The available priority
+                                processes. The available priority
                                 range depends on the selected CPU
-                                scheduling policy (see above). See
-                                <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
-                                for details.</para></listitem>
+                                scheduling policy (see above). For
+                                real-time scheduling policies an
+                                integer between 1 (lowest priority)
+                                and 99 (highest priority) can be used.
+                                See <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+                                for details.
+                                </para></listitem>
                         </varlistentry>
 
                         <varlistentry>

src/core/load-fragment.c

@@ -4,6 +4,7 @@
   This file is part of systemd.
 
   Copyright 2010 Lennart Poettering
+  Copyright 2012 Holger Hans Peter Freyther
 
   systemd is free software; you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published by
@@ -689,6 +690,8 @@ int config_parse_exec_cpu_sched_policy(
         }
 
         c->cpu_sched_policy = x;
+        /* Moving to or from real-time policy? We need to adjust the priority */
+        c->cpu_sched_priority = CLAMP(c->cpu_sched_priority, sched_get_priority_min(x), sched_get_priority_max(x));
         c->cpu_sched_set = true;
 
         return 0;
@@ -705,19 +708,28 @@ int config_parse_exec_cpu_sched_prio(
                 void *userdata) {
 
         ExecContext *c = data;
-        int i;
+        int i, min, max;
 
         assert(filename);
         assert(lvalue);
         assert(rvalue);
         assert(data);
 
-        /* On Linux RR/FIFO have the same range */
-        if (safe_atoi(rvalue, &i) < 0 || i < sched_get_priority_min(SCHED_RR) || i > sched_get_priority_max(SCHED_RR)) {
+        if (safe_atoi(rvalue, &i) < 0) {
                 log_error("[%s:%u] Failed to parse CPU scheduling priority, ignoring: %s", filename, line, rvalue);
                 return 0;
         }
 
+
+        /* On Linux RR/FIFO range from 1 to 99 and OTHER/BATCH may only be 0 */
+        min = sched_get_priority_min(c->cpu_sched_policy);
+        max = sched_get_priority_max(c->cpu_sched_policy);
+
+        if (i < min || i > max) {
+                log_error("[%s:%u] CPU scheduling priority is out of range, ignoring: %s", filename, line, rvalue);
+                return 0;
+        }
+
         c->cpu_sched_priority = i;
         c->cpu_sched_set = true;
 

src/test/test-sched-prio.c

@@ -0,0 +1,86 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Holger Hans Peter Freyther
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <sched.h>
+
+#include "manager.h"
+
+
+int main(int argc, char *argv[]) {
+        Manager *m;
+        Unit *idle_ok, *idle_bad, *rr_ok, *rr_bad, *rr_sched;
+        Service *ser;
+        FILE *serial = NULL;
+        FDSet *fdset = NULL;
+
+        /* prepare the test */
+        assert_se(set_unit_path(TEST_DIR) >= 0);
+        assert_se(manager_new(SYSTEMD_SYSTEM, &m) >= 0);
+        assert_se(manager_startup(m, serial, fdset) >= 0);
+
+        /* load idle ok */
+        assert_se(manager_load_unit(m, "sched_idle_ok.service", NULL, NULL, &idle_ok) >= 0);
+        assert_se(idle_ok->load_state == UNIT_LOADED);
+        ser = SERVICE(idle_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_OTHER);
+        assert_se(ser->exec_context.cpu_sched_priority == 0);
+
+        /*
+         * load idle bad. This should print a warning but we have no way to look at it.
+         */
+        assert_se(manager_load_unit(m, "sched_idle_bad.service", NULL, NULL, &idle_bad) >= 0);
+        assert_se(idle_bad->load_state == UNIT_LOADED);
+        ser = SERVICE(idle_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_OTHER);
+        assert_se(ser->exec_context.cpu_sched_priority == 0);
+
+        /*
+         * load rr ok.
+         * Test that the default priority is moving from 0 to 1.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_ok.service", NULL, NULL, &rr_ok) >= 0);
+        assert_se(rr_ok->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_ok);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 1);
+
+        /*
+         * load rr bad.
+         * Test that the value of 0 and 100 is ignored.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_bad.service", NULL, NULL, &rr_bad) >= 0);
+        assert_se(rr_bad->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_bad);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 1);
+
+        /*
+         * load rr change.
+         * Test that anything between 1 and 99 can be set.
+         */
+        assert_se(manager_load_unit(m, "sched_rr_change.service", NULL, NULL, &rr_sched) >= 0);
+        assert_se(rr_sched->load_state == UNIT_LOADED);
+        ser = SERVICE(rr_sched);
+        assert_se(ser->exec_context.cpu_sched_policy == SCHED_RR);
+        assert_se(ser->exec_context.cpu_sched_priority == 99);
+
+        return 0;
+}

test/sched_idle_bad.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Bad sched priority for Idle
+
+[Service]
+ExecStart=/bin/true
+CPUSchedulingPriority=1

test/sched_idle_ok.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Sched idle with prio 0
+
+[Service]
+ExecStart=/bin/true
+CPUSchedulingPriority=0

test/sched_rr_bad.service

@@ -0,0 +1,8 @@
+[Unit]
+Description=Bad sched priority for RR
+
+[Service]
+ExecStart=/bin/true
+CPUSchedulingPolicy=rr
+CPUSchedulingPriority=0
+CPUSchedulingPriority=100

test/sched_rr_change.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=Change prio
+
+[Service]
+ExecStart=/bin/true
+CPUSchedulingPolicy=rr
+CPUSchedulingPriority=1
+CPUSchedulingPriority=2
+CPUSchedulingPriority=99

test/sched_rr_ok.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Default prio for RR
+
+[Service]
+ExecStart=/bin/true
+CPUSchedulingPolicy=rr