linux-kernel - Re: [PATCH] power: process: use explicit levels for printk continuations

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Date:   Mon, 21 Nov 2022 17:09:21 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Weißschuh <linux@...ssschuh.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] power: process: use explicit levels for printk
 continuations

On Mon 2022-11-21 06:09:46, Thomas Weißschuh wrote:
> Many of the printk messages emitted during suspend and resume are
> emitted in fragments using pr_cont()/KERN_CONT.
> 
> As during suspend and resume a lot of operations are happing in the
> kernel the chances are high that the fragments are interspersed with
> unrelated messages.
> 
> In this case if no explicit level is specified for the fragments the
> standard level is applied, which by default is KERN_WARNING.
> 
> If the user is only observing KERN_WARNING and *not* KERN_INFO messages
> they will see incomplete message fragments.
> 
> By specifing the correct printk level also with the continuations this
> mismatch can be avoided.
> Also it reduces the amount of false-positive KERN_WARNING messages.

Yup, it is a known printk() limitation and this is the most reliable
solution.

> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  kernel/power/process.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index ddd9988327fe..0a828edc6d30 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -101,7 +101,7 @@ static int try_to_freeze_tasks(bool user_only)
>  			read_unlock(&tasklist_lock);
>  		}
>  	} else {
> -		pr_cont("(elapsed %d.%03d seconds) ", elapsed_msecs / 1000,
> +		pr_info(KERN_CONT "(elapsed %d.%03d seconds) ", elapsed_msecs / 1000,

It looks a bit ugly. Feel free to provide separate patch introducing
pr_<level>_cont() wrappers. Then you could use pr_info_cont() here.

We already have pr_<level>_once() and pr_<level>_ratelimited().
So pr_<level>_cont() would fit the existing pattern.


>  			elapsed_msecs % 1000);
>  	}
>  

Best Regards,
Petr