RE: [PREEMPT_RT][PATCH] printk: Enhance the condition check of msleep in pr_flush()

As John Ogness commented, I also found it would hang if sleep when >= SYSTEM_SCHEDULING.

 And as in commit https://lore.kernel.org/lkml/20170516184736.272225698@linutronix.de/ (local),  it should enable sleep right when the scheduler starts working(>= SYSTEM_RUNNING).

-Chao.

-----Original Message-----
From: John Ogness <john.ogness@linutronix.de> 
Sent: Friday, July 30, 2021 10:47 PM
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Qin, Chao <redacted>; linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org; tglx@linutronix.de; rostedt@goodmis.org; mgross@linux.intel.com; Mei, Paul <redacted>; Li, Lili <redacted>
Subject: Re: [PREEMPT_RT][PATCH] printk: Enhance the condition check of msleep in pr_flush()

On 2021-07-30, Sebastian Andrzej Siewior [off-list ref] wrote:

On 2021-07-19 17:01:51 [+0206], John Ogness wrote:

quoted

On 2021-07-19, chao.qin@intel.com wrote:

quoted

--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c

@@ -3620,7 +3620,8 @@ bool pr_flush(int timeout_ms, bool reset_on_progress)
 	u64 diff;
 	u64 seq;
 
-	may_sleep = (preemptible() && !in_softirq());
+	may_sleep = (preemptible() && !in_softirq()
+			&& (system_state >= SYSTEM_RUNNING));

I don't have more context but scheduling should work starting with 
SYSTEM_SCHEDULING.

I also thought this, but a quick test shows that is not the case. For example, init/main.c:kernel_init() is called in preemptible context, but
msleep() will hang if called at the beginning of that function.

John Ogness