selftests/livepatch: simplify test-klp-callbacks busy target tests

The test-klp-callbacks script includes a few tests which rely on kernel
task timings that may not always execute as expected under system load.
These may generate out of sequence kernel log messages that result in
test failure.

Instead of using sleep timing windows to orchestrate these tests, add a
block_transition module parameter to communicate the test purpose and
utilize flush_queue() to serialize the test module's task output.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200603182058.109470-2-ycote@redhat.com

1 files changed, 28 insertions, 9 deletions

diff --git a/lib/livepatch/test_klp_callbacks_busy.c b/lib/livepatch/test_klp_callbacks_busy.c
index 40beddf8a0e2..7ac845f65be5 100644
--- a/lib/livepatch/test_klp_callbacks_busy.c
+++ b/lib/livepatch/test_klp_callbacks_busy.c
@@ -5,34 +5,53 @@
 
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/sched.h>
 #include <linux/workqueue.h>
 #include <linux/delay.h>
 
-static int sleep_secs;
-module_param(sleep_secs, int, 0644);
-MODULE_PARM_DESC(sleep_secs, "sleep_secs (default=0)");
+/* load/run-time control from sysfs writer  */
+static bool block_transition;
+module_param(block_transition, bool, 0644);
+MODULE_PARM_DESC(block_transition, "block_transition (default=false)");
 
 static void busymod_work_func(struct work_struct *work);
-static DECLARE_DELAYED_WORK(work, busymod_work_func);
+static DECLARE_WORK(work, busymod_work_func);
 
 static void busymod_work_func(struct work_struct *work)
 {
-	pr_info("%s, sleeping %d seconds ...\n", __func__, sleep_secs);
-	msleep(sleep_secs * 1000);
+	pr_info("%s enter\n", __func__);
+
+	while (READ_ONCE(block_transition)) {
+		/*
+		 * Busy-wait until the sysfs writer has acknowledged a
+		 * blocked transition and clears the flag.
+		 */
+		msleep(20);
+	}
+
 	pr_info("%s exit\n", __func__);
 }
 
 static int test_klp_callbacks_busy_init(void)
 {
 	pr_info("%s\n", __func__);
-	schedule_delayed_work(&work,
-		msecs_to_jiffies(1000 * 0));
+	schedule_work(&work);
+
+	if (!block_transition) {
+		/*
+		 * Serialize output: print all messages from the work
+		 * function before returning from init().
+		 */
+		flush_work(&work);
+	}
+
 	return 0;
 }
 
 static void test_klp_callbacks_busy_exit(void)
 {
-	cancel_delayed_work_sync(&work);
+	WRITE_ONCE(block_transition, false);
+	flush_work(&work);
 	pr_info("%s\n", __func__);
 }