Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull v5.10 RCU changes from Paul E. McKenney:

- Debugging for smp_call_function().

- Strict grace periods for KASAN.  The point of this series is to find
  RCU-usage bugs, so the corresponding new RCU_STRICT_GRACE_PERIOD
  Kconfig option depends on both DEBUG_KERNEL and RCU_EXPERT, and is
  further disabled by dfefault.  Finally, the help text includes
  a goodly list of scary caveats.

- New smp_call_function() torture test.

- Torture-test updates.

- Documentation updates.

- Miscellaneous fixes.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

22 files changed, 208 insertions, 69 deletions

diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf-ftrace.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale-ftrace.sh
index 7d3c2be66c64..d4bec538086d 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf-ftrace.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale-ftrace.sh
@@ -1,12 +1,12 @@
 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0+
 #
-# Analyze a given results directory for rcuperf performance measurements,
+# Analyze a given results directory for rcuscale performance measurements,
 # looking for ftrace data.  Exits with 0 if data was found, analyzed, and
-# printed.  Intended to be invoked from kvm-recheck-rcuperf.sh after
+# printed.  Intended to be invoked from kvm-recheck-rcuscale.sh after
 # argument checking.
 #
-# Usage: kvm-recheck-rcuperf-ftrace.sh resdir
+# Usage: kvm-recheck-rcuscale-ftrace.sh resdir
 #
 # Copyright (C) IBM Corporation, 2016
 #
diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale.sh
index db0375a57f28..aa745152a525 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuperf.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck-rcuscale.sh
@@ -1,9 +1,9 @@
 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0+
 #
-# Analyze a given results directory for rcuperf performance measurements.
+# Analyze a given results directory for rcuscale scalability measurements.
 #
-# Usage: kvm-recheck-rcuperf.sh resdir
+# Usage: kvm-recheck-rcuscale.sh resdir
 #
 # Copyright (C) IBM Corporation, 2016
 #
@@ -20,7 +20,7 @@ fi
 PATH=`pwd`/tools/testing/selftests/rcutorture/bin:$PATH; export PATH
 . functions.sh
 
-if kvm-recheck-rcuperf-ftrace.sh $i
+if kvm-recheck-rcuscale-ftrace.sh $i
 then
 	# ftrace data was successfully analyzed, call it good!
 	exit 0
@@ -30,12 +30,12 @@ configfile=`echo $i | sed -e 's/^.*\///'`
 
 sed -e 's/^\[[^]]*]//' < $i/console.log |
 awk '
-/-perf: .* gps: .* batches:/ {
+/-scale: .* gps: .* batches:/ {
 	ngps = $9;
 	nbatches = $11;
 }
 
-/-perf: .*writer-duration/ {
+/-scale: .*writer-duration/ {
 	gptimes[++n] = $5 / 1000.;
 	sum += $5 / 1000.;
 }
@@ -43,7 +43,7 @@ awk '
 END {
 	newNR = asort(gptimes);
 	if (newNR <= 0) {
-		print "No rcuperf records found???"
+		print "No rcuscale records found???"
 		exit;
 	}
 	pct50 = int(newNR * 50 / 100);
@@ -79,5 +79,5 @@ END {
 	print "99th percentile grace-period duration: " gptimes[pct99];
 	print "Maximum grace-period duration: " gptimes[newNR];
 	print "Grace periods: " ngps + 0 " Batches: " nbatches + 0 " Ratio: " ngps / nbatches;
-	print "Computed from rcuperf printk output.";
+	print "Computed from rcuscale printk output.";
 }'
diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck-scf.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck-scf.sh
new file mode 100755
index 000000000000..671bfee4fcef
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck-scf.sh
@@ -0,0 +1,38 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Analyze a given results directory for rcutorture progress.
+#
+# Usage: kvm-recheck-rcu.sh resdir
+#
+# Copyright (C) Facebook, 2020
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+i="$1"
+if test -d "$i" -a -r "$i"
+then
+	:
+else
+	echo Unreadable results directory: $i
+	exit 1
+fi
+. functions.sh
+
+configfile=`echo $i | sed -e 's/^.*\///'`
+nscfs="`grep 'scf_invoked_count ver:' $i/console.log 2> /dev/null | tail -1 | sed -e 's/^.* scf_invoked_count ver: //' -e 's/ .*$//' | tr -d '\015'`"
+if test -z "$nscfs"
+then
+	echo "$configfile ------- "
+else
+	dur="`sed -e 's/^.* scftorture.shutdown_secs=//' -e 's/ .*$//' < $i/qemu-cmd 2> /dev/null`"
+	if test -z "$dur"
+	then
+		rate=""
+	else
+		nscfss=`awk -v nscfs=$nscfs -v dur=$dur '
+			BEGIN { print nscfs / dur }' < /dev/null`
+		rate=" ($nscfss/s)"
+	fi
+	echo "${configfile} ------- ${nscfs} SCF handler invocations$rate"
+fi
diff --git a/tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh b/tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh
index e07779a62634..6dc2b49b85ea 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-test-1-run.sh
@@ -66,6 +66,7 @@ config_override_param () {
 echo > $T/KcList
 config_override_param "$config_dir/CFcommon" KcList "`cat $config_dir/CFcommon 2> /dev/null`"
 config_override_param "$config_template" KcList "`cat $config_template 2> /dev/null`"
+config_override_param "--gdb options" KcList "$TORTURE_KCONFIG_GDB_ARG"
 config_override_param "--kasan options" KcList "$TORTURE_KCONFIG_KASAN_ARG"
 config_override_param "--kcsan options" KcList "$TORTURE_KCONFIG_KCSAN_ARG"
 config_override_param "--kconfig argument" KcList "$TORTURE_KCONFIG_ARG"
@@ -152,7 +153,11 @@ qemu_append="`identify_qemu_append "$QEMU"`"
 boot_args="`configfrag_boot_params "$boot_args" "$config_template"`"
 # Generate kernel-version-specific boot parameters
 boot_args="`per_version_boot_params "$boot_args" $resdir/.config $seconds`"
-echo $QEMU $qemu_args -m $TORTURE_QEMU_MEM -kernel $KERNEL -append \"$qemu_append $boot_args\" > $resdir/qemu-cmd
+if test -n "$TORTURE_BOOT_GDB_ARG"
+then
+	boot_args="$boot_args $TORTURE_BOOT_GDB_ARG"
+fi
+echo $QEMU $qemu_args -m $TORTURE_QEMU_MEM -kernel $KERNEL -append \"$qemu_append $boot_args\" $TORTURE_QEMU_GDB_ARG > $resdir/qemu-cmd
 
 if test -n "$TORTURE_BUILDONLY"
 then
@@ -171,14 +176,26 @@ echo "NOTE: $QEMU either did not run or was interactive" > $resdir/console.log
 # Attempt to run qemu
 ( . $T/qemu-cmd; wait `cat  $resdir/qemu_pid`; echo $? > $resdir/qemu-retval ) &
 commandcompleted=0
-sleep 10 # Give qemu's pid a chance to reach the file
-if test -s "$resdir/qemu_pid"
+if test -z "$TORTURE_KCONFIG_GDB_ARG"
 then
-	qemu_pid=`cat "$resdir/qemu_pid"`
-	echo Monitoring qemu job at pid $qemu_pid
-else
-	qemu_pid=""
-	echo Monitoring qemu job at yet-as-unknown pid
+	sleep 10 # Give qemu's pid a chance to reach the file
+	if test -s "$resdir/qemu_pid"
+	then
+		qemu_pid=`cat "$resdir/qemu_pid"`
+		echo Monitoring qemu job at pid $qemu_pid
+	else
+		qemu_pid=""
+		echo Monitoring qemu job at yet-as-unknown pid
+	fi
+fi
+if test -n "$TORTURE_KCONFIG_GDB_ARG"
+then
+	echo Waiting for you to attach a debug session, for example: > /dev/tty
+	echo "    gdb $base_resdir/vmlinux" > /dev/tty
+	echo 'After symbols load and the "(gdb)" prompt appears:' > /dev/tty
+	echo "    target remote :1234" > /dev/tty
+	echo "    continue" > /dev/tty
+	kstarttime=`gawk 'BEGIN { print systime() }' < /dev/null`
 fi
 while :
 do
diff --git a/tools/testing/selftests/rcutorture/bin/kvm.sh b/tools/testing/selftests/rcutorture/bin/kvm.sh
index e655983b7429..6eb1d3f6524d 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm.sh
@@ -31,6 +31,9 @@ TORTURE_DEFCONFIG=defconfig
 TORTURE_BOOT_IMAGE=""
 TORTURE_INITRD="$KVM/initrd"; export TORTURE_INITRD
 TORTURE_KCONFIG_ARG=""
+TORTURE_KCONFIG_GDB_ARG=""
+TORTURE_BOOT_GDB_ARG=""
+TORTURE_QEMU_GDB_ARG=""
 TORTURE_KCONFIG_KASAN_ARG=""
 TORTURE_KCONFIG_KCSAN_ARG=""
 TORTURE_KMAKE_ARG=""
@@ -46,6 +49,7 @@ jitter="-1"
 
 usage () {
 	echo "Usage: $scriptname optional arguments:"
+	echo "       --allcpus"
 	echo "       --bootargs kernel-boot-arguments"
 	echo "       --bootimage relative-path-to-kernel-boot-image"
 	echo "       --buildonly"
@@ -55,17 +59,19 @@ usage () {
 	echo "       --defconfig string"
 	echo "       --dryrun sched|script"
 	echo "       --duration minutes"
+	echo "       --gdb"
+	echo "       --help"
 	echo "       --interactive"
 	echo "       --jitter N [ maxsleep (us) [ maxspin (us) ] ]"
 	echo "       --kconfig Kconfig-options"
 	echo "       --kmake-arg kernel-make-arguments"
 	echo "       --mac nn:nn:nn:nn:nn:nn"
-	echo "       --memory megabytes | nnnG"
+	echo "       --memory megabytes|nnnG"
 	echo "       --no-initrd"
 	echo "       --qemu-args qemu-arguments"
 	echo "       --qemu-cmd qemu-system-..."
 	echo "       --results absolute-pathname"
-	echo "       --torture rcu"
+	echo "       --torture lock|rcu|rcuscale|refscale|scf"
 	echo "       --trust-make"
 	exit 1
 }
@@ -126,6 +132,14 @@ do
 		dur=$(($2*60))
 		shift
 		;;
+	--gdb)
+		TORTURE_KCONFIG_GDB_ARG="CONFIG_DEBUG_INFO=y"; export TORTURE_KCONFIG_GDB_ARG
+		TORTURE_BOOT_GDB_ARG="nokaslr"; export TORTURE_BOOT_GDB_ARG
+		TORTURE_QEMU_GDB_ARG="-s -S"; export TORTURE_QEMU_GDB_ARG
+		;;
+	--help|-h)
+		usage
+		;;
 	--interactive)
 		TORTURE_QEMU_INTERACTIVE=1; export TORTURE_QEMU_INTERACTIVE
 		;;
@@ -184,13 +198,13 @@ do
 		shift
 		;;
 	--torture)
-		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuperf\|refscale\)$' '^--'
+		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|scf\)$' '^--'
 		TORTURE_SUITE=$2
 		shift
-		if test "$TORTURE_SUITE" = rcuperf || test "$TORTURE_SUITE" = refscale
+		if test "$TORTURE_SUITE" = rcuscale || test "$TORTURE_SUITE" = refscale
 		then
 			# If you really want jitter for refscale or
-			# rcuperf, specify it after specifying the rcuperf
+			# rcuscale, specify it after specifying the rcuscale
 			# or the refscale.  (But why jitter in these cases?)
 			jitter=0
 		fi
@@ -248,6 +262,15 @@ do
 done
 touch $T/cfgcpu
 configs_derep="`echo $configs_derep | sed -e "s/\<CFLIST\>/$defaultconfigs/g"`"
+if test -n "$TORTURE_KCONFIG_GDB_ARG"
+then
+	if test "`echo $configs_derep | wc -w`" -gt 1
+	then
+		echo "The --config list is: $configs_derep."
+		echo "Only one --config permitted with --gdb, terminating."
+		exit 1
+	fi
+fi
 for CF1 in $configs_derep
 do
 	if test -f "$CONFIGFRAG/$CF1"
@@ -323,6 +346,9 @@ TORTURE_BUILDONLY="$TORTURE_BUILDONLY"; export TORTURE_BUILDONLY
 TORTURE_DEFCONFIG="$TORTURE_DEFCONFIG"; export TORTURE_DEFCONFIG
 TORTURE_INITRD="$TORTURE_INITRD"; export TORTURE_INITRD
 TORTURE_KCONFIG_ARG="$TORTURE_KCONFIG_ARG"; export TORTURE_KCONFIG_ARG
+TORTURE_KCONFIG_GDB_ARG="$TORTURE_KCONFIG_GDB_ARG"; export TORTURE_KCONFIG_GDB_ARG
+TORTURE_BOOT_GDB_ARG="$TORTURE_BOOT_GDB_ARG"; export TORTURE_BOOT_GDB_ARG
+TORTURE_QEMU_GDB_ARG="$TORTURE_QEMU_GDB_ARG"; export TORTURE_QEMU_GDB_ARG
 TORTURE_KCONFIG_KASAN_ARG="$TORTURE_KCONFIG_KASAN_ARG"; export TORTURE_KCONFIG_KASAN_ARG
 TORTURE_KCONFIG_KCSAN_ARG="$TORTURE_KCONFIG_KCSAN_ARG"; export TORTURE_KCONFIG_KCSAN_ARG
 TORTURE_KMAKE_ARG="$TORTURE_KMAKE_ARG"; export TORTURE_KMAKE_ARG
diff --git a/tools/testing/selftests/rcutorture/bin/parse-console.sh b/tools/testing/selftests/rcutorture/bin/parse-console.sh
index 71a9f43a3918..e03338091a06 100755
--- a/tools/testing/selftests/rcutorture/bin/parse-console.sh
+++ b/tools/testing/selftests/rcutorture/bin/parse-console.sh
@@ -33,8 +33,8 @@ then
 fi
 cat /dev/null > $file.diags
 
-# Check for proper termination, except for rcuperf and refscale.
-if test "$TORTURE_SUITE" != rcuperf && test "$TORTURE_SUITE" != refscale
+# Check for proper termination, except for rcuscale and refscale.
+if test "$TORTURE_SUITE" != rcuscale && test "$TORTURE_SUITE" != refscale
 then
 	# check for abject failure
 
@@ -67,6 +67,7 @@ then
 	grep --binary-files=text 'torture:.*ver:' $file |
 	egrep --binary-files=text -v '\(null\)|rtc: 000000000* ' |
 	sed -e 's/^(initramfs)[^]]*] //' -e 's/^\[[^]]*] //' |
+	sed -e 's/^.*ver: //' |
 	awk '
 	BEGIN	{
 		ver = 0;
@@ -74,13 +75,13 @@ then
 		}
 
 		{
-		if (!badseq && ($5 + 0 != $5 || $5 <= ver)) {
+		if (!badseq && ($1 + 0 != $1 || $1 <= ver)) {
 			badseqno1 = ver;
-			badseqno2 = $5;
+			badseqno2 = $1;
 			badseqnr = NR;
 			badseq = 1;
 		}
-		ver = $5
+		ver = $1
 		}
 
 	END	{
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE05 b/tools/testing/selftests/rcutorture/configs/rcu/TREE05
index 2dde0d9964e3..4f95f8544f3f 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE05
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE05
@@ -16,5 +16,6 @@ CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
+CONFIG_PROVE_RCU_LIST=y
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/CFcommon b/tools/testing/selftests/rcutorture/configs/rcuperf/CFcommon
deleted file mode 100644
index a09816b8c0f3..000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/CFcommon
+++ /dev/null
@@ -1,2 +0,0 @@
-CONFIG_RCU_PERF_TEST=y
-CONFIG_PRINTK_TIME=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/CFLIST b/tools/testing/selftests/rcutorture/configs/rcuscale/CFLIST
index c9f56cf20775..c9f56cf20775 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/CFLIST
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/CFLIST
diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon b/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon
new file mode 100644
index 000000000000..87caa0e932c7
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon
@@ -0,0 +1,2 @@
+CONFIG_RCU_SCALE_TEST=y
+CONFIG_PRINTK_TIME=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/TINY b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY
index fb05ef5279b4..fb05ef5279b4 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/TINY
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/TREE b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE
index 721cfda76ab2..721cfda76ab2 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/TREE
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/TREE54 b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54
index 7629f5dd73b2..7629f5dd73b2 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/TREE54
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54
diff --git a/tools/testing/selftests/rcutorture/configs/rcuperf/ver_functions.sh b/tools/testing/selftests/rcutorture/configs/rcuscale/ver_functions.sh
index 777d5b0c190f..0333e9b18522 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuperf/ver_functions.sh
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/ver_functions.sh
@@ -11,6 +11,6 @@
 #
 # Adds per-version torture-module parameters to kernels supporting them.
 per_version_boot_params () {
-	echo $1 rcuperf.shutdown=1 \
-		rcuperf.verbose=1
+	echo $1 rcuscale.shutdown=1 \
+		rcuscale.verbose=1
 }
diff --git a/tools/testing/selftests/rcutorture/configs/scf/CFLIST b/tools/testing/selftests/rcutorture/configs/scf/CFLIST
new file mode 100644
index 000000000000..4d62eb4a39f9
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/CFLIST
@@ -0,0 +1,2 @@
+NOPREEMPT
+PREEMPT
diff --git a/tools/testing/selftests/rcutorture/configs/scf/CFcommon b/tools/testing/selftests/rcutorture/configs/scf/CFcommon
new file mode 100644
index 000000000000..c11ab91f49f5
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/CFcommon
@@ -0,0 +1,2 @@
+CONFIG_SCF_TORTURE_TEST=y
+CONFIG_PRINTK_TIME=y
diff --git a/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT b/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT
new file mode 100644
index 000000000000..b8429d6c6ebc
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT
@@ -0,0 +1,9 @@
+CONFIG_SMP=y
+CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=n
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=n
+CONFIG_NO_HZ_FULL=y
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_PROVE_LOCKING=n
diff --git a/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT.boot b/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT.boot
new file mode 100644
index 000000000000..d6a7fa097c2e
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT.boot
@@ -0,0 +1 @@
+nohz_full=1
diff --git a/tools/testing/selftests/rcutorture/configs/scf/PREEMPT b/tools/testing/selftests/rcutorture/configs/scf/PREEMPT
new file mode 100644
index 000000000000..ae4992b141b0
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/PREEMPT
@@ -0,0 +1,9 @@
+CONFIG_SMP=y
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+CONFIG_HZ_PERIODIC=n
+CONFIG_NO_HZ_IDLE=y
+CONFIG_NO_HZ_FULL=n
+CONFIG_DEBUG_LOCK_ALLOC=y
+CONFIG_PROVE_LOCKING=y
diff --git a/tools/testing/selftests/rcutorture/configs/scf/ver_functions.sh b/tools/testing/selftests/rcutorture/configs/scf/ver_functions.sh
new file mode 100644
index 000000000000..d3d9e35d3d55
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/scf/ver_functions.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Torture-suite-dependent shell functions for the rest of the scripts.
+#
+# Copyright (C) Facebook, 2020
+#
+# Authors: Paul E. McKenney <paulmck@kernel.org>
+
+# scftorture_param_onoff bootparam-string config-file
+#
+# Adds onoff scftorture module parameters to kernels having it.
+scftorture_param_onoff () {
+	if ! bootparam_hotplug_cpu "$1" && configfrag_hotplug_cpu "$2"
+	then
+		echo CPU-hotplug kernel, adding scftorture onoff. 1>&2
+		echo scftorture.onoff_interval=1000 scftorture.onoff_holdoff=30
+	fi
+}
+
+# per_version_boot_params bootparam-string config-file seconds
+#
+# Adds per-version torture-module parameters to kernels supporting them.
+per_version_boot_params () {
+	echo $1 `scftorture_param_onoff "$1" "$2"` \
+		scftorture.stat_interval=15 \
+		scftorture.shutdown_secs=$3 \
+		scftorture.verbose=1 \
+		scf
+}
diff --git a/tools/testing/selftests/rcutorture/doc/initrd.txt b/tools/testing/selftests/rcutorture/doc/initrd.txt
index 933b4fd12327..41a4255865d4 100644
--- a/tools/testing/selftests/rcutorture/doc/initrd.txt
+++ b/tools/testing/selftests/rcutorture/doc/initrd.txt
@@ -1,12 +1,11 @@
-The rcutorture scripting tools automatically create the needed initrd
-directory using dracut.  Failing that, this tool will create an initrd
-containing a single statically linked binary named "init" that loops
-over a very long sleep() call.  In both cases, this creation is done
-by tools/testing/selftests/rcutorture/bin/mkinitrd.sh.
+The rcutorture scripting tools automatically create an initrd containing
+a single statically linked binary named "init" that loops over a
+very long sleep() call.  In both cases, this creation is done by
+tools/testing/selftests/rcutorture/bin/mkinitrd.sh.
 
-However, if you are attempting to run rcutorture on a system that does
-not have dracut installed, and if you don't like the notion of static
-linking, you might wish to press an existing initrd into service:
+However, if you don't like the notion of statically linked bare-bones
+userspace environments, you might wish to press an existing initrd
+into service:
 
 ------------------------------------------------------------------------
 cd tools/testing/selftests/rcutorture
@@ -15,24 +14,3 @@ mkdir initrd
 cd initrd
 cpio -id < /tmp/initrd.img.zcat
 # Manually verify that initrd contains needed binaries and libraries.
-------------------------------------------------------------------------
-
-Interestingly enough, if you are running rcutorture, you don't really
-need userspace in many cases.  Running without userspace has the
-advantage of allowing you to test your kernel independently of the
-distro in place, the root-filesystem layout, and so on.  To make this
-happen, put the following script in the initrd's tree's "/init" file,
-with 0755 mode.
-
-------------------------------------------------------------------------
-#!/bin/sh
-
-while :
-do
-	sleep 10
-done
-------------------------------------------------------------------------
-
-This approach also allows most of the binaries and libraries in the
-initrd filesystem to be dispensed with, which can save significant
-space in rcutorture's "res" directory.
diff --git a/tools/testing/selftests/rcutorture/doc/rcu-test-image.txt b/tools/testing/selftests/rcutorture/doc/rcu-test-image.txt
index 449cf579d6f9..b2fc247976b1 100644
--- a/tools/testing/selftests/rcutorture/doc/rcu-test-image.txt
+++ b/tools/testing/selftests/rcutorture/doc/rcu-test-image.txt
@@ -1,8 +1,33 @@
-This document describes one way to create the rcu-test-image file
-that contains the filesystem used by the guest-OS kernel.  There are
-probably much better ways of doing this, and this filesystem could no
-doubt be smaller.  It is probably also possible to simply download
-an appropriate image from any number of places.
+Normally, a minimal initrd is created automatically by the rcutorture
+scripting.  But minimal really does mean "minimal", namely just a single
+root directory with a single statically linked executable named "init":
+
+$ size tools/testing/selftests/rcutorture/initrd/init
+   text    data     bss     dec     hex filename
+    328       0       8     336     150 tools/testing/selftests/rcutorture/initrd/init
+
+Suppose you need to run some scripts, perhaps to monitor or control
+some aspect of the rcutorture testing.  This will require a more fully
+filled-out userspace, perhaps containing libraries, executables for
+the shell and other utilities, and soforth.  In that case, place your
+desired filesystem here:
+
+	tools/testing/selftests/rcutorture/initrd
+
+For example, your tools/testing/selftests/rcutorture/initrd/init might
+be a script that does any needed mount operations and starts whatever
+scripts need starting to properly monitor or control your testing.
+The next rcutorture build will then incorporate this filesystem into
+the kernel image that is passed to qemu.
+
+Or maybe you need a real root filesystem for some reason, in which case
+please read on!
+
+The remainder of this document describes one way to create the
+rcu-test-image file that contains the filesystem used by the guest-OS
+kernel.  There are probably much better ways of doing this, and this
+filesystem could no doubt be smaller.  It is probably also possible to
+simply download an appropriate image from any number of places.
 
 That said, here are the commands:
 
@@ -36,7 +61,7 @@ References:
 	https://help.ubuntu.com/community/JeOSVMBuilder
 	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough
 	http://www.moe.co.uk/2011/01/07/pci_add_option_rom-failed-to-find-romfile-pxe-rtl8139-bin/ -- "apt-get install kvm-pxe"
-	http://www.landley.net/writing/rootfs-howto.html
-	http://en.wikipedia.org/wiki/Initrd
-	http://en.wikipedia.org/wiki/Cpio
+	https://www.landley.net/writing/rootfs-howto.html
+	https://en.wikipedia.org/wiki/Initrd
+	https://en.wikipedia.org/wiki/Cpio
 	http://wiki.libvirt.org/page/UbuntuKVMWalkthrough