linux-kernel - RE: [PREEMPT_RT][PATCH] printk: Enhance the condition check of msleep in pr

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Date:   Mon, 2 Aug 2021 06:08:38 +0000
From:   "Qin, Chao" <chao.qin@...el.com>
To:     John Ogness <john.ogness@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mgross@...ux.intel.com" <mgross@...ux.intel.com>,
        "Mei, Paul" <paul.mei@...el.com>, "Li, Lili" <lili.li@...el.com>
Subject: 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/,  it should enable sleep right when the scheduler starts working(>= SYSTEM_RUNNING).

-Chao.

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

On 2021-07-30, Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
> On 2021-07-19 17:01:51 [+0206], John Ogness wrote:
>> On 2021-07-19, chao.qin@...el.com wrote:
>> > --- 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