Hi Kemeng, https://git-scm.com/docs/git-format-patch#_base_tree_information] url: https://github.com/intel-lab-lkp/linux/commits/Kemeng-Shi/block-bfq-properly-mark-bfqq-remained-idle/20230219-104312 base: https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next patch link: https://lore.kernel.org/r/20230219104309.1511562-18-shikemeng%40huaweicloud.com patch subject: [PATCH 17/17] block, bfq: remove unnecessary local variable __bfqq in bfq_setup_merge config: openrisc-randconfig-m041-20230219 (https://download.01.org/0day-ci/archive/20230220/202302200841.9zinyY7i-lkp@xxxxxxxxx/config) compiler: or1k-linux-gcc (GCC) 12.1.0 If you fix the issue, kindly add following tag where applicable | Reported-by: kernel test robot <lkp@xxxxxxxxx> | Reported-by: Dan Carpenter <error27@xxxxxxxxx> | Link: https://lore.kernel.org/r/202302200841.9zinyY7i-lkp@xxxxxxxxx/ New smatch warnings: block/bfq-iosched.c:2785 bfq_setup_merge() error: we previously assumed 'new_bfqq' could be null (see line 2766) Old smatch warnings: block/bfq-iosched.c:6195 __bfq_insert_request() warn: variable dereferenced before check 'bfqq' (see line 6191) vim +/new_bfqq +2785 block/bfq-iosched.c 36eca894832351 Arianna Avanzini 2017-04-12 2751 static struct bfq_queue * 36eca894832351 Arianna Avanzini 2017-04-12 2752 bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq) 36eca894832351 Arianna Avanzini 2017-04-12 2753 { 36eca894832351 Arianna Avanzini 2017-04-12 2754 int process_refs, new_process_refs; 36eca894832351 Arianna Avanzini 2017-04-12 2755 36eca894832351 Arianna Avanzini 2017-04-12 2756 /* 36eca894832351 Arianna Avanzini 2017-04-12 2757 * If there are no process references on the new_bfqq, then it is 36eca894832351 Arianna Avanzini 2017-04-12 2758 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain 36eca894832351 Arianna Avanzini 2017-04-12 2759 * may have dropped their last reference (not just their last process 36eca894832351 Arianna Avanzini 2017-04-12 2760 * reference). 36eca894832351 Arianna Avanzini 2017-04-12 2761 */ 36eca894832351 Arianna Avanzini 2017-04-12 2762 if (!bfqq_process_refs(new_bfqq)) 36eca894832351 Arianna Avanzini 2017-04-12 2763 return NULL; 36eca894832351 Arianna Avanzini 2017-04-12 2764 36eca894832351 Arianna Avanzini 2017-04-12 2765 /* Avoid a circular list and skip interim queue merges. */ 114533e1e26a36 Kemeng Shi 2023-02-19 @2766 while ((new_bfqq = new_bfqq->new_bfqq)) { 114533e1e26a36 Kemeng Shi 2023-02-19 2767 if (new_bfqq == bfqq) 36eca894832351 Arianna Avanzini 2017-04-12 2768 return NULL; 36eca894832351 Arianna Avanzini 2017-04-12 2769 } This now loops until new_bfqq is NULL. 36eca894832351 Arianna Avanzini 2017-04-12 2770 36eca894832351 Arianna Avanzini 2017-04-12 2771 process_refs = bfqq_process_refs(bfqq); 36eca894832351 Arianna Avanzini 2017-04-12 2772 new_process_refs = bfqq_process_refs(new_bfqq); What? 36eca894832351 Arianna Avanzini 2017-04-12 2773 /* 36eca894832351 Arianna Avanzini 2017-04-12 2774 * If the process for the bfqq has gone away, there is no 36eca894832351 Arianna Avanzini 2017-04-12 2775 * sense in merging the queues. 36eca894832351 Arianna Avanzini 2017-04-12 2776 */ 36eca894832351 Arianna Avanzini 2017-04-12 2777 if (process_refs == 0 || new_process_refs == 0) 36eca894832351 Arianna Avanzini 2017-04-12 2778 return NULL; 36eca894832351 Arianna Avanzini 2017-04-12 2779 c1cee4ab36acef Jan Kara 2022-04-01 2780 /* c1cee4ab36acef Jan Kara 2022-04-01 2781 * Make sure merged queues belong to the same parent. Parents could c1cee4ab36acef Jan Kara 2022-04-01 2782 * have changed since the time we decided the two queues are suitable c1cee4ab36acef Jan Kara 2022-04-01 2783 * for merging. c1cee4ab36acef Jan Kara 2022-04-01 2784 */ c1cee4ab36acef Jan Kara 2022-04-01 @2785 if (new_bfqq->entity.parent != bfqq->entity.parent) c1cee4ab36acef Jan Kara 2022-04-01 2786 return NULL; c1cee4ab36acef Jan Kara 2022-04-01 2787 36eca894832351 Arianna Avanzini 2017-04-12 2788 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d", 36eca894832351 Arianna Avanzini 2017-04-12 2789 new_bfqq->pid); 36eca894832351 Arianna Avanzini 2017-04-12 2790 36eca894832351 Arianna Avanzini 2017-04-12 2791 /* 36eca894832351 Arianna Avanzini 2017-04-12 2792 * Merging is just a redirection: the requests of the process 36eca894832351 Arianna Avanzini 2017-04-12 2793 * owning one of the two queues are redirected to the other queue. 36eca894832351 Arianna Avanzini 2017-04-12 2794 * The latter queue, in its turn, is set as shared if this is the 36eca894832351 Arianna Avanzini 2017-04-12 2795 * first time that the requests of some process are redirected to 36eca894832351 Arianna Avanzini 2017-04-12 2796 * it. 36eca894832351 Arianna Avanzini 2017-04-12 2797 * 6fa3e8d34204d5 Paolo Valente 2017-04-12 2798 * We redirect bfqq to new_bfqq and not the opposite, because 6fa3e8d34204d5 Paolo Valente 2017-04-12 2799 * we are in the context of the process owning bfqq, thus we 6fa3e8d34204d5 Paolo Valente 2017-04-12 2800 * have the io_cq of this process. So we can immediately 6fa3e8d34204d5 Paolo Valente 2017-04-12 2801 * configure this io_cq to redirect the requests of the 6fa3e8d34204d5 Paolo Valente 2017-04-12 2802 * process to new_bfqq. In contrast, the io_cq of new_bfqq is 6fa3e8d34204d5 Paolo Valente 2017-04-12 2803 * not available any more (new_bfqq->bic == NULL). 6fa3e8d34204d5 Paolo Valente 2017-04-12 2804 * 6fa3e8d34204d5 Paolo Valente 2017-04-12 2805 * Anyway, even in case new_bfqq coincides with the in-service 6fa3e8d34204d5 Paolo Valente 2017-04-12 2806 * queue, redirecting requests the in-service queue is the 6fa3e8d34204d5 Paolo Valente 2017-04-12 2807 * best option, as we feed the in-service queue with new 6fa3e8d34204d5 Paolo Valente 2017-04-12 2808 * requests close to the last request served and, by doing so, 6fa3e8d34204d5 Paolo Valente 2017-04-12 2809 * are likely to increase the throughput. 36eca894832351 Arianna Avanzini 2017-04-12 2810 */ 36eca894832351 Arianna Avanzini 2017-04-12 2811 bfqq->new_bfqq = new_bfqq; 15729ff8143f81 Paolo Valente 2021-11-25 2812 /* 15729ff8143f81 Paolo Valente 2021-11-25 2813 * The above assignment schedules the following redirections: 15729ff8143f81 Paolo Valente 2021-11-25 2814 * each time some I/O for bfqq arrives, the process that 15729ff8143f81 Paolo Valente 2021-11-25 2815 * generated that I/O is disassociated from bfqq and 15729ff8143f81 Paolo Valente 2021-11-25 2816 * associated with new_bfqq. Here we increases new_bfqq->ref 15729ff8143f81 Paolo Valente 2021-11-25 2817 * in advance, adding the number of processes that are 15729ff8143f81 Paolo Valente 2021-11-25 2818 * expected to be associated with new_bfqq as they happen to 15729ff8143f81 Paolo Valente 2021-11-25 2819 * issue I/O. 15729ff8143f81 Paolo Valente 2021-11-25 2820 */ 36eca894832351 Arianna Avanzini 2017-04-12 2821 new_bfqq->ref += process_refs; 36eca894832351 Arianna Avanzini 2017-04-12 2822 return new_bfqq; 36eca894832351 Arianna Avanzini 2017-04-12 2823 } -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests
