linux-kernel - Re: [PATCH] kernel/trace: Stop and wait for kthread on preempt irq module unload

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Date:   Tue, 28 Apr 2020 10:44:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xiao Yang <yangx.jy@...fujitsu.com>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kernel/trace: Stop and wait for kthread on preempt irq
 module unload

On Tue, 28 Apr 2020 18:19:05 +0800
Xiao Yang <yangx.jy@...fujitsu.com> wrote:

> Hi Joel,
> 
> Thanks for your quick fix.
> 
> Unfortunately, it fixes my original panic but introduces other
> issues(two wanings and one panic) on my arm64 vm, as below:
>

Does the following on top of Joel's patch fix it?

-- Steve

diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index 1c28ca20e30b..6d9131ae7e8c 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -113,15 +113,27 @@ static int preemptirq_delay_run(void *data)
 
 	for (i = 0; i < s; i++)
 		(testfuncs[i])(i);
+
+	while (!kthread_should_stop()) {
+		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
+	}
+
+	__set_current_state(TASK_RUNNING);
+
 	return 0;
 }
 
 static struct task_struct *preemptirq_start_test(void)
 {
+	struct task_struct *task;
 	char task_name[50];
 
 	snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
-	return kthread_run(preemptirq_delay_run, NULL, task_name);
+	task = kthread_run(preemptirq_delay_run, NULL, task_name);
+	if (IS_ERR(task))
+		return NULL;
+	return task;
 }