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

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Date:   Mon, 19 Jul 2021 17:01:51 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     chao.qin@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, bigeasy@...utronix.de,
        tglx@...utronix.de, rostedt@...dmis.org
Cc:     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 2021-07-19, chao.qin@...el.com wrote:
> From: Chao Qin <chao.qin@...el.com>
>
> There is msleep in pr_flush(). If call WARN() in the early boot
> stage such as in early_initcall, pr_flush() will run into msleep
> when process scheduler is not ready yet. And then the system will
> sleep forever.
>
> Before the system_state is SYSTEM_RUNNING, make sure DO NOT sleep
> in pr_flush().
>
> Fixes: 63cf1e4b564a ("printk: add pr_flush()")
>
> Signed-off-by: Chao Qin <chao.qin@...el.com>
> Signed-off-by: Lili Li <lili.li@...el.com>

Reviewed-by: John Ogness <john.ogness@...utronix.de>

> ---
>  kernel/printk/printk.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 209d2392f0d8..a9b3afbdac39 100644
> --- 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));
>  
>  	seq = prb_next_seq(prb);
>  
>
> base-commit: 7e175e6b59975c8901ad370f7818937f68de45c1
> -- 
> 2.25.1