[PATCH net] selftests: rtnetlink: try double sleep to give WQ a chance

[Jakub Kicinski <kuba@kernel.org>]

The rtnetlink test for preferred lifetime of an address is quite flaky.
Problems started around the 6.16 merge window in May. The test fails
with:

   FAIL: preferred_lft addresses remaining

and unlike most of our flakes this one fails on the "normal" kernel
builds, not the builds with kernel/configs/debug.config. I suspect
the flakes may be related to power saving, since the expirations
run from a "power efficient" workqueue. Adding a short sleep seems
to decrease the flakes by 8x but they still happen. With this
patch in place we get a flake every couple of weeks, not every
couple of days. Better ideas welcome..

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: liuhangbin@gmail.com
CC: shuah@kernel.org
CC: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/rtnetlink.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/net/rtnetlink.sh b/tools/testing/selftests/net/rtnetlink.sh
index 2e8243a65b50..b9e1497ea27a 100755
--- a/tools/testing/selftests/net/rtnetlink.sh
+++ b/tools/testing/selftests/net/rtnetlink.sh
@@ -299,6 +299,11 @@ kci_test_addrlft()
 	done
 
 	sleep 5
+	# Schedule out for a bit, address GC runs from the power efficient WQ
+	# if the long sleep above has put the whole system into sleep state
+	# the WQ may have not had a chance to run.
+	sleep 0.1
+
 	run_cmd_grep_fail "10.23.11." ip addr show dev "$devdummy"
 	if [ $? -eq 0 ]; then
 		check_err 1
-- 
2.50.0