tree: https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-5.12.y-rt-rebase head: 2664a7f5d3d24da4b2657a1e933181d376b77616 commit: bc04b285e73c1a64fd5d9723af20a21ce0feb628 [30/193] printk: use seqcount_latch for console_seq config: mips-randconfig-r016-20210318 (attached as .config) compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 436c6c9c20cc522c92a923440a5fc509c342a7db) reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # install mips cross compiling tool for clang build # apt-get install binutils-mips-linux-gnu # https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/com... git remote add linux-rt-devel https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git git fetch --no-tags linux-rt-devel linux-5.12.y-rt-rebase git checkout bc04b285e73c1a64fd5d9723af20a21ce0feb628 # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All errors (new ones prefixed by >>): In file included from kernel/printk/printk.c:62: kernel/printk/internal.h:56:20: warning: no previous prototype for function 'vprintk_func' [-Wmissing-prototypes] __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; } ^ kernel/printk/internal.h:56:16: note: declare 'static' if the function is not intended to be used outside of this translation unit __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; } ^ static kernel/printk/printk.c:176:5: warning: no previous prototype for function 'devkmsg_sysctl_set_loglvl' [-Wmissing-prototypes] int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, ^ kernel/printk/printk.c:176:1: note: declare 'static' if the function is not intended to be used outside of this translation unit int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, ^ static kernel/printk/printk.c:2288:2: error: FIXME #error FIXME ^ kernel/printk/printk.c:2648:9: error: implicit declaration of function 'latched_seq_read_nolock' [-Werror,-Wimplicit-function-declaration] seq = latched_seq_read_nolock(&console_seq); ^ latched_seq_write(&console_seq, r.info->seq); ^ kernel/printk/printk.c:2664:4: error: implicit declaration of function 'latched_seq_write' [-Werror,-Wimplicit-function-declaration] latched_seq_write(&console_seq, seq + 1); ^ kernel/printk/printk.c:2691:3: error: implicit declaration of function 'latched_seq_write' [-Werror,-Wimplicit-function-declaration] latched_seq_write(&console_seq, seq + 1); ^ kernel/printk/printk.c:2782:4: error: implicit declaration of function 'latched_seq_write' [-Werror,-Wimplicit-function-declaration] latched_seq_write(&console_seq, prb_first_valid_seq(prb)); ^ kernel/printk/printk.c:3029:32: error: implicit declaration of function 'latched_seq_read_nolock' [-Werror,-Wimplicit-function-declaration] exclusive_console_stop_seq = latched_seq_read_nolock(&console_seq); ^ kernel/printk/printk.c:3033:3: error: implicit declaration of function 'latched_seq_write' [-Werror,-Wimplicit-function-declaration] latched_seq_write(&console_seq, syslog_seq); ^ 2 warnings and 8 errors generated. vim +/latched_seq_write +2654 kernel/printk/printk.c 2582 2583 /** 2584 * console_unlock - unlock the console system 2585 * 2586 * Releases the console_lock which the caller holds on the console system 2587 * and the console driver list. 2588 * 2589 * While the console_lock was held, console output may have been buffered 2590 * by printk(). If this is the case, console_unlock(); emits 2591 * the output prior to releasing the lock. 2592 * 2593 * If there is output waiting, we wake /dev/kmsg and syslog() users. 2594 * 2595 * console_unlock(); may be called from any context. 2596 */ 2597 void console_unlock(void) 2598 { 2599 static char ext_text[CONSOLE_EXT_LOG_MAX]; 2600 static char text[CONSOLE_LOG_MAX]; 2601 unsigned long flags; 2602 bool do_cond_resched, retry; 2603 struct printk_info info; 2604 struct printk_record r; 2605 u64 seq; 2606 2607 if (console_suspended) { 2608 up_console_sem(); 2609 return; 2610 } 2611 2612 prb_rec_init_rd(&r, &info, text, sizeof(text)); 2613 2614 /* 2615 * Console drivers are called with interrupts disabled, so 2616 * @console_may_schedule should be cleared before; however, we may 2617 * end up dumping a lot of lines, for example, if called from 2618 * console registration path, and should invoke cond_resched() 2619 * between lines if allowable. Not doing so can cause a very long 2620 * scheduling stall on a slow console leading to RCU stall and 2621 * softlockup warnings which exacerbate the issue with more 2622 * messages practically incapacitating the system. 2623 * 2624 * console_trylock() is not able to detect the preemptive 2625 * context reliably. Therefore the value must be stored before 2626 * and cleared after the "again" goto label. 2627 */ 2628 do_cond_resched = console_may_schedule; 2629 again: 2630 console_may_schedule = 0; 2631 2632 /* 2633 * We released the console_sem lock, so we need to recheck if 2634 * cpu is online and (if not) is there at least one CON_ANYTIME 2635 * console. 2636 */ 2637 if (!can_use_console()) { 2638 console_locked = 0; 2639 up_console_sem(); 2640 return; 2641 } 2642 2643 for (;;) { 2644 size_t ext_len = 0; 2645 size_t len; 2646 2647 skip: 2648 seq = latched_seq_read_nolock(&console_seq); 2649 if (!prb_read_valid(prb, seq, &r)) 2650 break; 2651 2652 if (seq != r.info->seq) { 2653 console_dropped += r.info->seq - seq; 2655 seq = r.info->seq; 2656 } 2657 2658 if (suppress_message_printing(r.info->level)) { 2659 /* 2660 * Skip record we have buffered and already printed 2661 * directly to the console when we received it, and 2662 * record that has level above the console loglevel. 2663 */ 2664 latched_seq_write(&console_seq, seq + 1); 2665 goto skip; 2666 } 2667 2668 /* Output to all consoles once old messages replayed. */ 2669 if (unlikely(exclusive_console && 2670 seq >= exclusive_console_stop_seq)) { 2671 exclusive_console = NULL; 2672 } 2673 2674 /* 2675 * Handle extended console text first because later 2676 * record_print_text() will modify the record buffer in-place. 2677 */ 2678 if (nr_ext_console_drivers) { 2679 ext_len = info_print_ext_header(ext_text, 2680 sizeof(ext_text), 2681 r.info); 2682 ext_len += msg_print_ext_body(ext_text + ext_len, 2683 sizeof(ext_text) - ext_len, 2684 &r.text_buf[0], 2685 r.info->text_len, 2686 &r.info->dev_info); 2687 } 2688 len = record_print_text(&r, 2689 console_msg_format & MSG_FORMAT_SYSLOG, 2690 printk_time); 2691 latched_seq_write(&console_seq, seq + 1); 2692 2693 printk_safe_enter_irqsave(flags); 2694 2695 /* 2696 * While actively printing out messages, if another printk() 2697 * were to occur on another CPU, it may wait for this one to 2698 * finish. This task can not be preempted if there is a 2699 * waiter waiting to take over. 2700 */ 2701 console_lock_spinning_enable(); 2702 2703 stop_critical_timings(); /* don't trace print latency */ 2704 call_console_drivers(ext_text, ext_len, text, len); 2705 start_critical_timings(); 2706 2707 if (console_lock_spinning_disable_and_check()) { 2708 printk_safe_exit_irqrestore(flags); 2709 return; 2710 } 2711 2712 printk_safe_exit_irqrestore(flags); 2713 2714 if (do_cond_resched) 2715 cond_resched(); 2716 } 2717 2718 console_locked = 0; 2719 2720 up_console_sem(); 2721 2722 /* 2723 * Someone could have filled up the buffer again, so re-check if there's 2724 * something to flush. In case we cannot trylock the console_sem again, 2725 * there's a new owner and the console_unlock() from them will do the 2726 * flush, no worries. 2727 */ 2728 retry = prb_read_valid(prb, latched_seq_read_nolock(&console_seq), NULL); 2729 if (retry && console_trylock()) 2730 goto again; 2731 } 2732 EXPORT_SYMBOL(console_unlock); 2733 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org