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 11:06:21 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     zhe.he@...driver.com
Cc:     pmladek@...e.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 (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);
 
 			/* messages are gone, move to first one */
 			console_seq = log_first_seq;

---

Steven, Petr, any objections?

	-ss