kernel/workqueue.c:2798: warning: expecting prototype for flush_workqueue(). Prototype was for void() instead

From: kernel test robot
Date: Sun May 15 2022 - 22:39:44 EST

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tree: https://github.com/intel-lab-lkp/linux/commits/UPDATE-20220516-093322/Tetsuo-Handa/checkpatch-warn-about-flushing-system-wide-workqueues/20220425-073327
head: cd007363b7985a824de0ec5e05f0cb0705e59c88
commit: cd007363b7985a824de0ec5e05f0cb0705e59c88 workqueue: Wrap flush_workqueue() using a macro
date: 63 minutes ago
config: um-i386_defconfig (https://download.01.org/0day-ci/archive/20220516/202205161030.Dv3ad4T3-lkp@xxxxxxxxx/config)
compiler: gcc-11 (Debian 11.2.0-20) 11.2.0
reproduce (this is a W=1 build):
# https://github.com/intel-lab-lkp/linux/commit/cd007363b7985a824de0ec5e05f0cb0705e59c88
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review UPDATE-20220516-093322/Tetsuo-Handa/checkpatch-warn-about-flushing-system-wide-workqueues/20220425-073327
git checkout cd007363b7985a824de0ec5e05f0cb0705e59c88
# save the config file
mkdir build_dir && cp config build_dir/.config
make W=1 O=build_dir ARCH=um SUBARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

kernel/workqueue.c:2798: warning: Function parameter or member 'flush_workqueue' not described in 'void'
>> kernel/workqueue.c:2798: warning: expecting prototype for flush_workqueue(). Prototype was for void() instead

vim +2798 kernel/workqueue.c

^1da177e4c3f41 Linus Torvalds 2005-04-16 2789
0fcb78c22f0634 Rolf Eike Beer 2006-07-30 2790 /**
^1da177e4c3f41 Linus Torvalds 2005-04-16 2791 * flush_workqueue - ensure that any scheduled work has run to completion.
0fcb78c22f0634 Rolf Eike Beer 2006-07-30 2792 * @wq: workqueue to flush
^1da177e4c3f41 Linus Torvalds 2005-04-16 2793 *
c5aa87bbf4b23f Tejun Heo 2013-03-13 2794 * This function sleeps until all work items which were queued on entry
c5aa87bbf4b23f Tejun Heo 2013-03-13 2795 * have finished execution, but it is not livelocked by new incoming ones.
^1da177e4c3f41 Linus Torvalds 2005-04-16 2796 */
cd007363b7985a Tetsuo Handa 2022-05-16 2797 void (flush_workqueue)(struct workqueue_struct *wq)
^1da177e4c3f41 Linus Torvalds 2005-04-16 @2798 {
73f53c4aa732ec Tejun Heo 2010-06-29 2799 struct wq_flusher this_flusher = {
73f53c4aa732ec Tejun Heo 2010-06-29 2800 .list = LIST_HEAD_INIT(this_flusher.list),
73f53c4aa732ec Tejun Heo 2010-06-29 2801 .flush_color = -1,
fd1a5b04dfb899 Byungchul Park 2017-10-25 2802 .done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, wq->lockdep_map),
73f53c4aa732ec Tejun Heo 2010-06-29 2803 };
73f53c4aa732ec Tejun Heo 2010-06-29 2804 int next_color;
f293ea92007419 Oleg Nesterov 2007-05-09 2805
3347fa0928210d Tejun Heo 2016-09-16 2806 if (WARN_ON(!wq_online))
3347fa0928210d Tejun Heo 2016-09-16 2807 return;
3347fa0928210d Tejun Heo 2016-09-16 2808
87915adc3f0acd Johannes Berg 2018-08-22 2809 lock_map_acquire(&wq->lockdep_map);
87915adc3f0acd Johannes Berg 2018-08-22 2810 lock_map_release(&wq->lockdep_map);
87915adc3f0acd Johannes Berg 2018-08-22 2811
3c25a55daadc7e Lai Jiangshan 2013-03-25 2812 mutex_lock(&wq->mutex);
73f53c4aa732ec Tejun Heo 2010-06-29 2813
73f53c4aa732ec Tejun Heo 2010-06-29 2814 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2815 * Start-to-wait phase
73f53c4aa732ec Tejun Heo 2010-06-29 2816 */
73f53c4aa732ec Tejun Heo 2010-06-29 2817 next_color = work_next_color(wq->work_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2818
73f53c4aa732ec Tejun Heo 2010-06-29 2819 if (next_color != wq->flush_color) {
73f53c4aa732ec Tejun Heo 2010-06-29 2820 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2821 * Color space is not full. The current work_color
73f53c4aa732ec Tejun Heo 2010-06-29 2822 * becomes our flush_color and work_color is advanced
73f53c4aa732ec Tejun Heo 2010-06-29 2823 * by one.
73f53c4aa732ec Tejun Heo 2010-06-29 2824 */
6183c009f6cd94 Tejun Heo 2013-03-12 2825 WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
73f53c4aa732ec Tejun Heo 2010-06-29 2826 this_flusher.flush_color = wq->work_color;
73f53c4aa732ec Tejun Heo 2010-06-29 2827 wq->work_color = next_color;
73f53c4aa732ec Tejun Heo 2010-06-29 2828
73f53c4aa732ec Tejun Heo 2010-06-29 2829 if (!wq->first_flusher) {
73f53c4aa732ec Tejun Heo 2010-06-29 2830 /* no flush in progress, become the first flusher */
6183c009f6cd94 Tejun Heo 2013-03-12 2831 WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2832
73f53c4aa732ec Tejun Heo 2010-06-29 2833 wq->first_flusher = &this_flusher;
73f53c4aa732ec Tejun Heo 2010-06-29 2834
112202d9098aae Tejun Heo 2013-02-13 2835 if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
73f53c4aa732ec Tejun Heo 2010-06-29 2836 wq->work_color)) {
73f53c4aa732ec Tejun Heo 2010-06-29 2837 /* nothing to flush, done */
73f53c4aa732ec Tejun Heo 2010-06-29 2838 wq->flush_color = next_color;
73f53c4aa732ec Tejun Heo 2010-06-29 2839 wq->first_flusher = NULL;
73f53c4aa732ec Tejun Heo 2010-06-29 2840 goto out_unlock;
73f53c4aa732ec Tejun Heo 2010-06-29 2841 }
73f53c4aa732ec Tejun Heo 2010-06-29 2842 } else {
73f53c4aa732ec Tejun Heo 2010-06-29 2843 /* wait in queue */
6183c009f6cd94 Tejun Heo 2013-03-12 2844 WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2845 list_add_tail(&this_flusher.list, &wq->flusher_queue);
112202d9098aae Tejun Heo 2013-02-13 2846 flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2847 }
73f53c4aa732ec Tejun Heo 2010-06-29 2848 } else {
73f53c4aa732ec Tejun Heo 2010-06-29 2849 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2850 * Oops, color space is full, wait on overflow queue.
73f53c4aa732ec Tejun Heo 2010-06-29 2851 * The next flush completion will assign us
73f53c4aa732ec Tejun Heo 2010-06-29 2852 * flush_color and transfer to flusher_queue.
73f53c4aa732ec Tejun Heo 2010-06-29 2853 */
73f53c4aa732ec Tejun Heo 2010-06-29 2854 list_add_tail(&this_flusher.list, &wq->flusher_overflow);
73f53c4aa732ec Tejun Heo 2010-06-29 2855 }
73f53c4aa732ec Tejun Heo 2010-06-29 2856
fca839c00a12d6 Tejun Heo 2015-12-07 2857 check_flush_dependency(wq, NULL);
fca839c00a12d6 Tejun Heo 2015-12-07 2858
3c25a55daadc7e Lai Jiangshan 2013-03-25 2859 mutex_unlock(&wq->mutex);
73f53c4aa732ec Tejun Heo 2010-06-29 2860
73f53c4aa732ec Tejun Heo 2010-06-29 2861 wait_for_completion(&this_flusher.done);
73f53c4aa732ec Tejun Heo 2010-06-29 2862
73f53c4aa732ec Tejun Heo 2010-06-29 2863 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2864 * Wake-up-and-cascade phase
73f53c4aa732ec Tejun Heo 2010-06-29 2865 *
73f53c4aa732ec Tejun Heo 2010-06-29 2866 * First flushers are responsible for cascading flushes and
73f53c4aa732ec Tejun Heo 2010-06-29 2867 * handling overflow. Non-first flushers can simply return.
73f53c4aa732ec Tejun Heo 2010-06-29 2868 */
00d5d15b0641f4 Chris Wilson 2020-03-10 2869 if (READ_ONCE(wq->first_flusher) != &this_flusher)
73f53c4aa732ec Tejun Heo 2010-06-29 2870 return;
73f53c4aa732ec Tejun Heo 2010-06-29 2871
3c25a55daadc7e Lai Jiangshan 2013-03-25 2872 mutex_lock(&wq->mutex);
73f53c4aa732ec Tejun Heo 2010-06-29 2873
4ce48b37bfedc2 Tejun Heo 2010-07-02 2874 /* we might have raced, check again with mutex held */
4ce48b37bfedc2 Tejun Heo 2010-07-02 2875 if (wq->first_flusher != &this_flusher)
4ce48b37bfedc2 Tejun Heo 2010-07-02 2876 goto out_unlock;
4ce48b37bfedc2 Tejun Heo 2010-07-02 2877
00d5d15b0641f4 Chris Wilson 2020-03-10 2878 WRITE_ONCE(wq->first_flusher, NULL);
73f53c4aa732ec Tejun Heo 2010-06-29 2879
6183c009f6cd94 Tejun Heo 2013-03-12 2880 WARN_ON_ONCE(!list_empty(&this_flusher.list));
6183c009f6cd94 Tejun Heo 2013-03-12 2881 WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2882
73f53c4aa732ec Tejun Heo 2010-06-29 2883 while (true) {
73f53c4aa732ec Tejun Heo 2010-06-29 2884 struct wq_flusher *next, *tmp;
73f53c4aa732ec Tejun Heo 2010-06-29 2885
73f53c4aa732ec Tejun Heo 2010-06-29 2886 /* complete all the flushers sharing the current flush color */
73f53c4aa732ec Tejun Heo 2010-06-29 2887 list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
73f53c4aa732ec Tejun Heo 2010-06-29 2888 if (next->flush_color != wq->flush_color)
73f53c4aa732ec Tejun Heo 2010-06-29 2889 break;
73f53c4aa732ec Tejun Heo 2010-06-29 2890 list_del_init(&next->list);
73f53c4aa732ec Tejun Heo 2010-06-29 2891 complete(&next->done);
73f53c4aa732ec Tejun Heo 2010-06-29 2892 }
73f53c4aa732ec Tejun Heo 2010-06-29 2893
6183c009f6cd94 Tejun Heo 2013-03-12 2894 WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
73f53c4aa732ec Tejun Heo 2010-06-29 2895 wq->flush_color != work_next_color(wq->work_color));
73f53c4aa732ec Tejun Heo 2010-06-29 2896
73f53c4aa732ec Tejun Heo 2010-06-29 2897 /* this flush_color is finished, advance by one */
73f53c4aa732ec Tejun Heo 2010-06-29 2898 wq->flush_color = work_next_color(wq->flush_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2899
73f53c4aa732ec Tejun Heo 2010-06-29 2900 /* one color has been freed, handle overflow queue */
73f53c4aa732ec Tejun Heo 2010-06-29 2901 if (!list_empty(&wq->flusher_overflow)) {
73f53c4aa732ec Tejun Heo 2010-06-29 2902 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2903 * Assign the same color to all overflowed
73f53c4aa732ec Tejun Heo 2010-06-29 2904 * flushers, advance work_color and append to
73f53c4aa732ec Tejun Heo 2010-06-29 2905 * flusher_queue. This is the start-to-wait
73f53c4aa732ec Tejun Heo 2010-06-29 2906 * phase for these overflowed flushers.
73f53c4aa732ec Tejun Heo 2010-06-29 2907 */
73f53c4aa732ec Tejun Heo 2010-06-29 2908 list_for_each_entry(tmp, &wq->flusher_overflow, list)
73f53c4aa732ec Tejun Heo 2010-06-29 2909 tmp->flush_color = wq->work_color;
73f53c4aa732ec Tejun Heo 2010-06-29 2910
73f53c4aa732ec Tejun Heo 2010-06-29 2911 wq->work_color = work_next_color(wq->work_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2912
73f53c4aa732ec Tejun Heo 2010-06-29 2913 list_splice_tail_init(&wq->flusher_overflow,
73f53c4aa732ec Tejun Heo 2010-06-29 2914 &wq->flusher_queue);
112202d9098aae Tejun Heo 2013-02-13 2915 flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2916 }
73f53c4aa732ec Tejun Heo 2010-06-29 2917
73f53c4aa732ec Tejun Heo 2010-06-29 2918 if (list_empty(&wq->flusher_queue)) {
6183c009f6cd94 Tejun Heo 2013-03-12 2919 WARN_ON_ONCE(wq->flush_color != wq->work_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2920 break;
73f53c4aa732ec Tejun Heo 2010-06-29 2921 }
73f53c4aa732ec Tejun Heo 2010-06-29 2922
73f53c4aa732ec Tejun Heo 2010-06-29 2923 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2924 * Need to flush more colors. Make the next flusher
112202d9098aae Tejun Heo 2013-02-13 2925 * the new first flusher and arm pwqs.
73f53c4aa732ec Tejun Heo 2010-06-29 2926 */
6183c009f6cd94 Tejun Heo 2013-03-12 2927 WARN_ON_ONCE(wq->flush_color == wq->work_color);
6183c009f6cd94 Tejun Heo 2013-03-12 2928 WARN_ON_ONCE(wq->flush_color != next->flush_color);
73f53c4aa732ec Tejun Heo 2010-06-29 2929
73f53c4aa732ec Tejun Heo 2010-06-29 2930 list_del_init(&next->list);
73f53c4aa732ec Tejun Heo 2010-06-29 2931 wq->first_flusher = next;
73f53c4aa732ec Tejun Heo 2010-06-29 2932
112202d9098aae Tejun Heo 2013-02-13 2933 if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
73f53c4aa732ec Tejun Heo 2010-06-29 2934 break;
73f53c4aa732ec Tejun Heo 2010-06-29 2935
73f53c4aa732ec Tejun Heo 2010-06-29 2936 /*
73f53c4aa732ec Tejun Heo 2010-06-29 2937 * Meh... this color is already done, clear first
73f53c4aa732ec Tejun Heo 2010-06-29 2938 * flusher and repeat cascading.
73f53c4aa732ec Tejun Heo 2010-06-29 2939 */
73f53c4aa732ec Tejun Heo 2010-06-29 2940 wq->first_flusher = NULL;
73f53c4aa732ec Tejun Heo 2010-06-29 2941 }
73f53c4aa732ec Tejun Heo 2010-06-29 2942
73f53c4aa732ec Tejun Heo 2010-06-29 2943 out_unlock:
3c25a55daadc7e Lai Jiangshan 2013-03-25 2944 mutex_unlock(&wq->mutex);
^1da177e4c3f41 Linus Torvalds 2005-04-16 2945 }
1dadafa86a7798 Tim Gardner 2015-08-04 2946 EXPORT_SYMBOL(flush_workqueue);
^1da177e4c3f41 Linus Torvalds 2005-04-16 2947

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