torture: Use "jittering" file to control jitter.sh execution

Currently, jitter.sh execution is controlled by a time limit and by the
"kill" command.  The former allowed jitter.sh to run uselessly past
the end of a set of runs that panicked during boot, and the latter is
vulnerable to PID reuse.  This commit therefore introduces a "jittering"
file in the date-stamp directory within "res" that must be present for
the jitter.sh scripts to continue executing.  The time limit is still
in place in order to avoid disturbing runs featuring large trace dumps,
but the removal of the "jittering" file handles the panic-during-boot
scenario without relying on PIDs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

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

@@ -5,10 +5,11 @@
 # of this script is to inflict random OS jitter on a concurrently running
 # test.
 #
-# Usage: jitter.sh me duration [ sleepmax [ spinmax ] ]
+# Usage: jitter.sh me duration jittering-path [ sleepmax [ spinmax ] ]
 #
 # me: Random-number-generator seed salt.
 # duration: Time to run in seconds.
+# jittering-path: Path to file whose removal will stop this script.
 # sleepmax: Maximum microseconds to sleep, defaults to one second.
 # spinmax: Maximum microseconds to spin, defaults to one millisecond.
 #
@@ -18,8 +19,9 @@
 
 me=$(($1 * 1000))
 duration=$2
-sleepmax=${3-1000000}
-spinmax=${4-1000}
+jittering=$3
+sleepmax=${4-1000000}
+spinmax=${5-1000}
 
 n=1
 
@@ -47,7 +49,7 @@ do
 	fi
 
 	# Check for stop request.
-	if test -f "$TORTURE_STOPFILE"
+	if ! test -f "$jittering"
 	then
 		exit 1;
 	fi

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

@@ -503,14 +503,17 @@ function dump(first, pastlast, batchnum)
 	print "then"
 	print "\techo ---- Starting kernels. `date` | tee -a " rd "log";
 	print "\techo > " rd "jitter_pids"
+	print "\ttouch " rd "jittering"
 	for (j = 0; j < njitter; j++) {
-		print "\tjitter.sh " j " " dur " " ja[2] " " ja[3] "&"
+		print "\tjitter.sh " j " " dur " " rd "jittering " ja[2] " " ja[3] "&"
 		print "\techo $! >> " rd "jitter_pids"
 	}
 	print "\twhile ls $runfiles > /dev/null 2>&1"
 	print "\tdo"
 	print "\t\t:"
 	print "\tdone"
+	print "\trm -f " rd "jittering"
+	print "\twait"
 	print "\techo ---- All kernel runs complete. `date` | tee -a " rd "log";
 	print "else"
 	print "\twait"