torture: Use elapsed time to detect hangs

The kvm-test-1-run.sh currently counts "sleep 1" commands to detect
hangs.  This can fail spectacularly on busy systems, where "sleep 1"
might take far longer than one second to complete.  This commit
therefore changes hang detection to use elapsed time measurements.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

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

@@ -167,14 +167,18 @@ fi
 qemu_pid=$!
 commandcompleted=0
 echo Monitoring qemu job at pid $qemu_pid
-for ((i=0;i<$seconds;i++))
+while :
 do
+	kruntime=`awk 'BEGIN { print systime() - '"$kstarttime"' }' < /dev/null`
 	if kill -0 $qemu_pid > /dev/null 2>&1
 	then
+		if test $kruntime -ge $seconds
+		then
+			break;
+		fi
 		sleep 1
 	else
 		commandcompleted=1
-		kruntime=`awk 'BEGIN { print systime() - '"$kstarttime"' }' < /dev/null`
 		if test $kruntime -lt $seconds
 		then
 			echo Completed in $kruntime vs. $seconds >> $resdir/Warnings 2>&1
@@ -194,20 +198,22 @@ done
 if test $commandcompleted -eq 0
 then
 	echo Grace period for qemu job at pid $qemu_pid
-	for ((i=0;i<=$grace;i++))
+	while :
 	do
+		kruntime=`awk 'BEGIN { print systime() - '"$kstarttime"' }' < /dev/null`
 		if kill -0 $qemu_pid > /dev/null 2>&1
 		then
-			sleep 1
+			:
 		else
 			break
 		fi
-		if test $i -eq $grace
+		if test $kruntime -ge $((seconds + grace))
 		then
-			kruntime=`awk 'BEGIN { print systime() - '"$kstarttime"' }'`
 			echo "!!! Hang at $kruntime vs. $seconds seconds" >> $resdir/Warnings 2>&1
 			kill -KILL $qemu_pid
+			break
 		fi
+		sleep 1
 	done
 fi