rcutorture: Specify MAXSMP=y for TREE01

Setting CONFIG_MAXSMP=y causes cpumasks to be moved offstack, which
introduces the possibility of NULL cpumask_var_t pointers.  This commit
therefore enables CONFIG_MAXSMP=y in TREE01 to increase test coverage.
However, because CONFIG_MAXSMP=y implies 8192 CPUs, we need to use
the maxcpus= boot parameter to limit the number of CPUs to something
reasonable, which in turn requires updating the scripts to handle this.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>

tools/testing/selftests/rcutorture/bin/functions.sh

@@ -64,6 +64,26 @@ configfrag_boot_params () {
 	fi
 }
 
+# configfrag_boot_cpus bootparam-string config-fragment-file config-cpus
+#
+# Decreases number of CPUs based on any maxcpus= boot parameters specified.
+configfrag_boot_cpus () {
+	local bootargs="`configfrag_boot_params "$1" "$2"`"
+	local maxcpus
+	if echo "${bootargs}" | grep -q 'maxcpus=[0-9]'
+	then
+		maxcpus="`echo "${bootargs}" | sed -e 's/^.*maxcpus=\([0-9]*\).*$/\1/'`"
+		if test "$3" -gt "$maxcpus"
+		then
+			echo $maxcpus
+		else
+			echo $3
+		fi
+	else
+		echo $3
+	fi
+}
+
 # configfrag_hotplug_cpu config-fragment-file
 #
 # Returns 1 if the config fragment specifies hotplug CPU.

tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh

@@ -140,6 +140,7 @@ fi
 # Generate -smp qemu argument.
 qemu_args="-nographic $qemu_args"
 cpu_count=`configNR_CPUS.sh $config_template`
+cpu_count=`configfrag_boot_cpus "$boot_args" "$config_template" "$cpu_count"`
 vcpus=`identify_qemu_vcpus`
 if test $cpu_count -gt $vcpus
 then

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -188,7 +188,9 @@ for CF in $configs
 do
 	if test -f "$CONFIGFRAG/$kversion/$CF"
 	then
-		echo $CF `configNR_CPUS.sh $CONFIGFRAG/$kversion/$CF` >> $T/cfgcpu
+		cpu_count=`configNR_CPUS.sh $CONFIGFRAG/$kversion/$CF`
+		cpu_count=`configfrag_boot_cpus "$TORTURE_BOOTARGS" "$CONFIGFRAG/$kversion/$CF" "$cpu_count"`
+		echo $CF $cpu_count >> $T/cfgcpu
 	else
 		echo "The --configs file $CF does not exist, terminating."
 		exit 1

tools/testing/selftests/rcutorture/configs/rcu/TREE01

 CONFIG_SMP=y
-CONFIG_NR_CPUS=8
 CONFIG_PREEMPT_NONE=n
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=y
@@ -10,8 +9,7 @@ CONFIG_NO_HZ_FULL=n
 CONFIG_RCU_FAST_NO_HZ=y
 CONFIG_RCU_TRACE=y
 CONFIG_HOTPLUG_CPU=y
-CONFIG_RCU_FANOUT=8
-CONFIG_RCU_FANOUT_EXACT=n
+CONFIG_MAXSMP=y
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_RCU_NOCB_CPU_ZERO=y
 CONFIG_DEBUG_LOCK_ALLOC=n

tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot

-rcutorture.torture_type=rcu_bh
+rcutorture.torture_type=rcu_bh maxcpus=8