[PATCH v4 16/17] selftests/verification: Rearrange the wwnr_printk test

[Gabriele Monaco <gmonaco@redhat.com>]

The wwnr_printk test expects no reactions in some situations, after
fixing the bash assertion, the test is failing because expecting no
reaction after a previous step had reactions is flaky without making
sure all buffers are flushed.

Wait for reactions to be over when expected by polling dmesg for an
interval without any rv message.
Also simplify the load function to stop loads as soon as a reaction
occurs, this limits the number of lines to flush and makes tests overall
faster and more stable.

Reviewed-by: Wen Yang <wen.yang@linux.dev>
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---

Notes:
    V4:
    * Wait for dmesg to flush all messages after reactions

 .../verification/test.d/rv_wwnr_printk.tc     | 23 ++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc b/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc
index 96de95edb530..37d96e1ae93b 100644
--- a/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc
+++ b/tools/testing/selftests/verification/test.d/rv_wwnr_printk.tc
@@ -4,23 +4,40 @@
 # requires: available_reactors wwnr:monitor printk:reactor stress-ng:program
 
 load() { # returns true if there was a reaction
-	local lines_before num
+	local lines_before num load_pid ret
 	num=$((($(nproc) + 1) / 2))
 	lines_before=$(dmesg | wc -l)
-	stress-ng --cpu-sched "$num" --timer "$num" -t 5 -q
-	dmesg | tail -n $((lines_before + 1)) | grep -q "rv: monitor wwnr does not allow event"
+	stress-ng --cpu-sched "$num" --timer "$num" -t 5 -q &
+	load_pid=$!
+	timeout 5 dmesg -w | tail -n +$((lines_before + 1)) | grep -m 1 -q "rv: monitor wwnr does not allow event"
+	ret=$?
+	kill "$load_pid" || true
+	wait "$load_pid" || true
+	return $ret
+}
+
+# loads may flood the ringbuffer, wait for all pending printks
+wait_dmesg_flush() {
+	local last_before last_after=$(dmesg | grep "rv:" | tail -n 1 || true)
+	while [ "$last_before" != "$last_after" ]; do
+		last_before=$last_after
+		sleep .3
+		last_after=$(dmesg | grep "rv:" | tail -n 1 || true)
+	done
 }
 
 echo 1 > monitors/wwnr/enable
 echo printk > monitors/wwnr/reactors
 
 load
+wait_dmesg_flush
 
 echo 0 > monitoring_on
 ! load || false
 echo 1 > monitoring_on
 
 load
+wait_dmesg_flush
 
 echo 0 > reacting_on
 ! load || false
-- 
2.55.0