[PATCH] selftests/net: deflake GRO tests and fix return value and output

[Kevin Krakauer <krakauer@xxxxxxxxxx>]

GRO tests are timing dependent and can easily flake. This is partially
mitigated in gro.sh by giving each subtest 3 chances to pass. However,
this still flakes on some machines.

Set the device's napi_defer_hard_irqs to 50 so that GRO is less likely
to immediately flush. This already happened in setup_loopback.sh, but
wasn't added to setup_veth.sh. This accounts for most of the reduction
in flakiness.

We also increase the number of chances for success from 3 to 6.

`gro.sh -t <test>` now returns a passing/failing exit code as expected.

gro.c:main no longer erroneously claims a test passes when running as a
server.

Tested: Ran `gro.sh -t large` 100 times with and without this change.
Passed 100/100 with and 64/100 without. Ran inside strace to increase
flakiness.

Signed-off-by: Kevin Krakauer <krakauer@xxxxxxxxxx>
---
 tools/testing/selftests/net/gro.c         | 8 +++++---
 tools/testing/selftests/net/gro.sh        | 5 +++--
 tools/testing/selftests/net/setup_veth.sh | 1 +
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/net/gro.c b/tools/testing/selftests/net/gro.c
index b2184847e388..d5824eadea10 100644
--- a/tools/testing/selftests/net/gro.c
+++ b/tools/testing/selftests/net/gro.c
@@ -1318,11 +1318,13 @@ int main(int argc, char **argv)
 	read_MAC(src_mac, smac);
 	read_MAC(dst_mac, dmac);
 
-	if (tx_socket)
+	if (tx_socket) {
 		gro_sender();
-	else
+	} else {
+		/* Only the receiver exit status determines test success. */
 		gro_receiver();
+		fprintf(stderr, "Gro::%s test passed.\n", testname);
+	}
 
-	fprintf(stderr, "Gro::%s test passed.\n", testname);
 	return 0;
 }
diff --git a/tools/testing/selftests/net/gro.sh b/tools/testing/selftests/net/gro.sh
index 02c21ff4ca81..703173f8c8a9 100755
--- a/tools/testing/selftests/net/gro.sh
+++ b/tools/testing/selftests/net/gro.sh
@@ -21,7 +21,7 @@ run_test() {
   # Each test is run 3 times to deflake, because given the receive timing,
   # not all packets that should coalesce will be considered in the same flow
   # on every try.
-  for tries in {1..3}; do
+  for tries in {1..6}; do
     # Actual test starts here
     ip netns exec $server_ns ./gro "${ARGS[@]}" "--rx" "--iface" "server" \
       1>>log.txt &
@@ -100,5 +100,6 @@ trap cleanup EXIT
 if [[ "${test}" == "all" ]]; then
   run_all_tests
 else
-  run_test "${proto}" "${test}"
+  exit_code=$(run_test "${proto}" "${test}")
+  exit $exit_code
 fi;
diff --git a/tools/testing/selftests/net/setup_veth.sh b/tools/testing/selftests/net/setup_veth.sh
index 1f78a87f6f37..9882ad730c24 100644
--- a/tools/testing/selftests/net/setup_veth.sh
+++ b/tools/testing/selftests/net/setup_veth.sh
@@ -12,6 +12,7 @@ setup_veth_ns() {
 
 	[[ -e /var/run/netns/"${ns_name}" ]] || ip netns add "${ns_name}"
 	echo 1000000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
+	echo 50 > "/sys/class/net/${ns_dev}/napi_defer_hard_irqs"
 	ip link set dev "${ns_dev}" netns "${ns_name}" mtu 65535
 	ip -netns "${ns_name}" link set dev "${ns_dev}" up
 
-- 
2.48.1