Messages in this thread | | | From | John Ogness <> | Subject | Re: [PATCH printk v3 6/6] printk: introduce console_prepend_dropped() for dropped messages | Date | Thu, 05 Jan 2023 15:01:28 +0106 |
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On 2023-01-05, kernel test robot <lkp@intel.com> wrote: > smatch warnings: > kernel/printk/printk.c:2735 console_prepend_dropped() warn: always true condition '(cmsg->outbuf_len + len >= outbuf_sz) => (0-u64max >= 0)'
Thank you kernel test robot, but actually this code will never be hit when outbuf_sz is 0. Explanation below.
> 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;
If outbuf_sz is 0, the above check will return. It is interesting that smatch did not complain about this line instead. I suppose the WARN_ON_ONCE confused it.
Note that if outbuf_sz is 0, then CONFIG_PRINTK is undefined. In that case this function should not be called anyway. So the check and warning are appropriate here.
> 2734 >> 2735 if (cmsg->outbuf_len + len >= outbuf_sz) {
John Ogness
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