torture: Kill qemu, not parent process

The current hang-check machinery in the rcutorture scripts uses "$!" of
a parenthesized bash statement to capture the pid.  Unfortunately, this
captures not qemu's pid, but rather that of its parent that implements
the parenthesized statement.  This commit therefore adjusts things so as
to capture qemu's actual pid, which then allows the script to actually
kill qemu in event of a kernel hang.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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

@@ -168,14 +168,25 @@ then
 fi
 echo "NOTE: $QEMU either did not run or was interactive" > $resdir/console.log
 echo $QEMU $qemu_args -m 512 -kernel $resdir/bzImage -append \"$qemu_append $boot_args\" > $resdir/qemu-cmd
-( $QEMU $qemu_args -m 512 -kernel $resdir/bzImage -append "$qemu_append $boot_args"; echo $? > $resdir/qemu-retval ) &
-qemu_pid=$!
+( $QEMU $qemu_args -m 512 -kernel $resdir/bzImage -append "$qemu_append $boot_args"& echo $! > $resdir/qemu_pid; wait `cat  $resdir/qemu_pid`; echo $? > $resdir/qemu-retval ) &
 commandcompleted=0
-echo Monitoring qemu job at pid $qemu_pid
+sleep 10 # Give qemu's pid a chance to reach the file
+if test -s "$resdir/qemu_pid"
+then
+	qemu_pid=`cat "$resdir/qemu_pid"`
+	echo Monitoring qemu job at pid $qemu_pid
+else
+	qemu_pid=""
+	echo Monitoring qemu job at yet-as-unknown pid
+fi
 while :
 do
+	if test -z "$qemu_pid" -a -s "$resdir/qemu_pid"
+	then
+		qemu_pid=`cat "$resdir/qemu_pid"`
+	fi
 	kruntime=`awk 'BEGIN { print systime() - '"$kstarttime"' }' < /dev/null`
-	if kill -0 $qemu_pid > /dev/null 2>&1
+	if test -z "$qemu_pid" || kill -0 "$qemu_pid" > /dev/null 2>&1
 	then
 		if test $kruntime -ge $seconds
 		then
@@ -195,12 +206,16 @@ do
 				ps -fp $killpid >> $resdir/Warnings 2>&1
 			fi
 		else
-			echo ' ---' `date`: Kernel done
+			echo ' ---' `date`: "Kernel done"
 		fi
 		break
 	fi
 done
-if test $commandcompleted -eq 0
+if test -z "$qemu_pid" -a -s "$resdir/qemu_pid"
+then
+	qemu_pid=`cat "$resdir/qemu_pid"`
+fi
+if test $commandcompleted -eq 0 -a -n "$qemu_pid"
 then
 	echo Grace period for qemu job at pid $qemu_pid
 	while :
@@ -220,6 +235,9 @@ then
 		fi
 		sleep 1
 	done
+elif test -z "$qemu_pid"
+then
+	echo Unknown PID, cannot kill qemu command
 fi
 
 parse-torture.sh $resdir/console.log $title