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

[Qin, Chao]

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@xxxxxxxxxxxxx/,  it should enable sleep right when the scheduler starts working(>= SYSTEM_RUNNING).

-Chao.

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

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