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BUG: KCSAN: data-race in __blk_mq_sched_dispatch_requests / blk_mq_run_hw_queue

write to 0xffff8881295f7410 of 8 bytes by task 3254 on cpu 0:
 INIT_LIST_HEAD include/linux/list.h:36 [inline]
 list_splice_init include/linux/list.h:483 [inline]
 __blk_mq_sched_dispatch_requests+0x16a/0x2a0 block/blk-mq-sched.c:295
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:347
 __blk_mq_run_hw_queue+0xee/0x1c0 block/blk-mq.c:1525
 __blk_mq_delay_run_hw_queue+0x199/0x340 block/blk-mq.c:1602
 blk_mq_run_hw_queue+0x231/0x260 block/blk-mq.c:1655
 blk_mq_run_hw_queues block/blk-mq.c:1673 [inline]
 blk_mq_requeue_work+0x423/0x490 block/blk-mq.c:816
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881295f7410 of 8 bytes by task 30575 on cpu 1:
 list_empty_careful include/linux/list.h:319 [inline]
 blk_mq_hctx_has_pending block/blk-mq.c:72 [inline]
 blk_mq_run_hw_queue+0x12e/0x260 block/blk-mq.c:1651
 blk_mq_sched_insert_requests+0x14d/0x200 block/blk-mq-sched.c:601
 blk_mq_flush_plug_list+0x2f5/0x420 block/blk-mq.c:1924
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1867
 blk_finish_plug+0x44/0x60 block/blk-core.c:1884
 ext4_writepages+0x18cd/0x1ef0 fs/ext4/inode.c:2833
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19b/0x1d0 mm/filemap.c:422
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:761
 ext4_sync_file+0xfc/0x6e0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2734 [inline]
 ext4_buffered_write_iter+0x369/0x3b0 fs/ext4/file.c:277
 ext4_file_write_iter+0x57b/0x1000 fs/ext4/file.c:498
 call_write_iter include/linux/fs.h:1872 [inline]
 do_iter_readv_writev+0x32e/0x3d0 fs/read_write.c:713
 do_iter_write+0x112/0x4b0 fs/read_write.c:1018
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1601 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 30575 Comm: syz-executor.3 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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