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

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Date:   Fri, 30 Jul 2021 16:52:42 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     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, paul.mei@...el.com,
        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