[tip: core/rcu] torture: Make jitter.sh handle large systems

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     8126c57f00cea3502a017b7c76df1fac58f89e88
Gitweb:        https://git.kernel.org/tip/8126c57f00cea3502a017b7c76df1fac58f89e88
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Wed, 10 Feb 2021 13:25:58 -08:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 08 Mar 2021 14:21:41 -08:00

torture: Make jitter.sh handle large systems

The current jitter.sh script expects cpumask bits to fit into whatever
the awk interpreter uses for an integer, which clearly does not hold for
even medium-sized systems these days.  This means that on a large system,
only the first 32 or 64 CPUs (depending) are subjected to jitter.sh
CPU-time perturbations.  This commit therefore computes a given CPU's
cpumask using text manipulation rather than arithmetic shifts.

Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 tools/testing/selftests/rcutorture/bin/jitter.sh | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/jitter.sh b/tools/testing/selftests/rcutorture/bin/jitter.sh
index 188b864..3a856ec 100755
--- a/tools/testing/selftests/rcutorture/bin/jitter.sh
+++ b/tools/testing/selftests/rcutorture/bin/jitter.sh
@@ -67,10 +67,10 @@ do
 		srand(n + me + systime());
 		ncpus = split(cpus, ca);
 		curcpu = ca[int(rand() * ncpus + 1)];
-		mask = lshift(1, curcpu);
-		if (mask + 0 <= 0)
-			mask = 1;
-		printf("%#x\n", mask);
+		z = "";
+		for (i = 1; 4 * i <= curcpu; i++)
+			z = z "0";
+		print "0x" 2 ^ (curcpu % 4) z;
 	}' < /dev/null`
 	n=$(($n+1))
 	if ! taskset -p $cpumask $$ > /dev/null 2>&1