linux-kernel - Re: [PATCH v2 2/2] printk: Add KBUILD_MODNAME and correct bare use of unsigned

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Date:   Wed, 19 Sep 2018 13:20:18 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     zhe.he@...driver.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] printk: Add KBUILD_MODNAME and correct bare use
 of unsigned

On Wed 2018-09-19 11:06:21, Sergey Senozhatsky wrote:
> On (09/19/18 01:17), zhe.he@...driver.com wrote:
> > Add KBUILD_MODNAME to make prints more clear.
> 
> No strong opinion. I'm OK with this change.
> 
> > And use 'unsigned int' intead of 'unsigned' according to
> > checkpatch.pl's suggestion.
> 
> I don't think that "unsigned int" is the right thing to use there.
> 
> >  		if (console_seq < log_first_seq) {
> >  			len = sprintf(text, "** %u printk messages dropped **\n",
> > -				      (unsigned)(log_first_seq - console_seq));
> > +				   (unsigned int)(log_first_seq - console_seq));
> 
> Both log_first_seq and console_seq are u64.
> 
> 	log_first_seq - console_seq
> 
> thus, *in theory*, can be larger than "unsigned int". So I'd just avoid cast
> and use an appropriate for u64 %llu sprintf() specifier. Something like below,
> perhaps:
> 
> ---
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index f73ea9dd6f46..4b8c5832bf14 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2408,8 +2408,9 @@ void console_unlock(void)
>  		printk_safe_enter_irqsave(flags);
>  		raw_spin_lock(&logbuf_lock);
>  		if (console_seq < log_first_seq) {
> -			len = sprintf(text, "** %u printk messages dropped **\n",
> -				   (unsigned int)(log_first_seq - console_seq));
> +			len = sprintf(text,
> +				      "** %llu printk messages dropped **\n",
> +				      log_first_seq - console_seq);

This looks like a better solution.

Also please, define pr_fmt and fix the casting in separate patches.

Best Regards,
Petr