Revert "sched/debug: Remove the /proc/sys/kernel/sched_child_runs_first sysctl"

This reverts commit 17e7170645.

There are loads of CTS tests that want to see this proc file present in
order to "pass".  So, fake them out and just put it back, it's not been
hooked up to anything for a long time, so it isn't hurting anything to
put it back.

Odds are no one will even notice it...

Change-Id: If70527d377ffaabaa9e796153e4c735c1cf66de1
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

kernel/sched/debug.c

@@ -862,6 +862,7 @@ static void sched_debug_header(struct seq_file *m)
 #define PN(x) \
 	SEQ_printf(m, "  .%-40s: %Ld.%06ld\n", #x, SPLIT_NS(x))
 	PN(sysctl_sched_base_slice);
+	P(sysctl_sched_child_runs_first);
 	P(sysctl_sched_features);
 #undef PN
 #undef P

kernel/sched/fair.c

@@ -94,6 +94,12 @@ unsigned int sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;
 unsigned int sysctl_sched_base_slice			= 750000ULL;
 static unsigned int normalized_sysctl_sched_base_slice	= 750000ULL;
 
+/*
+ * After fork, child runs first. If set to 0 (default) then
+ * parent will (try to) run first.
+ */
+unsigned int sysctl_sched_child_runs_first __read_mostly;
+
 const_debug unsigned int sysctl_sched_migration_cost	= 500000UL;
 
 int sched_thermal_decay_shift;
@@ -155,6 +161,13 @@ static unsigned int sysctl_numa_balancing_promote_rate_limit = 65536;
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table sched_fair_sysctls[] = {
+	{
+		.procname       = "sched_child_runs_first",
+		.data           = &sysctl_sched_child_runs_first,
+		.maxlen         = sizeof(unsigned int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
 #ifdef CONFIG_CFS_BANDWIDTH
 	{
 		.procname       = "sched_cfs_bandwidth_slice_us",

kernel/sched/sched.h

@@ -102,6 +102,8 @@ extern __read_mostly int scheduler_running;
 extern unsigned long calc_load_update;
 extern atomic_long_t calc_load_tasks;
 
+extern unsigned int sysctl_sched_child_runs_first;
+
 extern void calc_global_load_tick(struct rq *this_rq);
 extern long calc_load_fold_active(struct rq *this_rq, long adjust);