linux-kernel - Re: [PATCH printk v3 6/6] printk: introduce console_prepend

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Date:   Thu, 5 Jan 2023 21:14:03 +0800
From:   kernel test robot <lkp@...el.com>
To:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>
Cc:     oe-kbuild-all@...ts.linux.dev,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v3 6/6] printk: introduce
 console_prepend_dropped() for dropped messages

Hi John,

I love your patch! Perhaps something to improve:

[auto build test WARNING on 6b2b0d839acaa84f05a77184370f793752e786e9]

url:    https://github.com/intel-lab-lkp/linux/commits/John-Ogness/printk-cleanup-buffer-handling/20221222-044216
base:   6b2b0d839acaa84f05a77184370f793752e786e9
patch link:    https://lore.kernel.org/r/20221221202704.857925-7-john.ogness%40linutronix.de
patch subject: [PATCH printk v3 6/6] printk: introduce console_prepend_dropped() for dropped messages
config: loongarch-randconfig-m031-20230103
compiler: loongarch64-linux-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>

smatch warnings:
kernel/printk/printk.c:2735 console_prepend_dropped() warn: always true condition '(cmsg->outbuf_len + len >= outbuf_sz) => (0-u64max >= 0)'

vim +2735 kernel/printk/printk.c

  2701	
  2702	/*
  2703	 * Prepend the message in @cmsg->cbufs->outbuf with a "dropped message". This
  2704	 * is achieved by shifting the existing message over and inserting the dropped
  2705	 * message.
  2706	 *
  2707	 * @cmsg is the console message to prepend.
  2708	 *
  2709	 * @dropped is the dropped count to report in the dropped message.
  2710	 *
  2711	 * If the message text in @cmsg->cbufs->outbuf does not have enough space for
  2712	 * the dropped message, the message text will be sufficiently truncated.
  2713	 *
  2714	 * If @cmsg->cbufs->outbuf is modified, @cmsg->outbuf_len is updated.
  2715	 */
  2716	static void console_prepend_dropped(struct console_message *cmsg, unsigned long dropped)
  2717	{
  2718		struct console_buffers *cbufs = cmsg->cbufs;
  2719		const size_t scratchbuf_sz = sizeof(cbufs->scratchbuf);
  2720		const size_t outbuf_sz = sizeof(cbufs->outbuf);
  2721		char *scratchbuf = &cbufs->scratchbuf[0];
  2722		char *outbuf = &cbufs->outbuf[0];
  2723		size_t len;
  2724	
  2725		len = snprintf(scratchbuf, scratchbuf_sz,
  2726			       "** %lu printk messages dropped **\n", dropped);
  2727	
  2728		/*
  2729		 * Make sure outbuf is sufficiently large before prepending. Space
  2730		 * for a terminator is also counted in case truncation occurs.
  2731		 */
  2732		if (WARN_ON_ONCE(len + 1 >= outbuf_sz))
  2733			return;
  2734	
> 2735		if (cmsg->outbuf_len + len >= outbuf_sz) {
  2736			/* Truncate the message, but keep it terminated. */
  2737			cmsg->outbuf_len = outbuf_sz - (len + 1);
  2738			outbuf[cmsg->outbuf_len] = 0;
  2739		}
  2740	
  2741		memmove(outbuf + len, outbuf, cmsg->outbuf_len + 1);
  2742		memcpy(outbuf, scratchbuf, len);
  2743		cmsg->outbuf_len += len;
  2744	}
  2745	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests

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