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BUG: KCSAN: data-race in __blk_mq_sched_dispatch_requests / blk_mq_run_hw_queue

write to 0xffff88810277c810 of 8 bytes by task 968 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/0x2c0 block/blk-mq-sched.c:299
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:351
 __blk_mq_run_hw_queue+0xbc/0x140 block/blk-mq.c:1499
 __blk_mq_delay_run_hw_queue+0x163/0x2f0 block/blk-mq.c:1576
 blk_mq_run_hw_queue+0x22c/0x250 block/blk-mq.c:1629
 blk_mq_run_hw_queues+0x1d1/0x230 block/blk-mq.c:1692
 blk_mq_requeue_work+0x3e6/0x420 block/blk-mq.c:798
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2275
 worker_thread+0x636/0xae0 kernel/workqueue.c:2421
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88810277c810 of 8 bytes by task 7681 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+0x129/0x250 block/blk-mq.c:1625
 blk_mq_sched_insert_request+0x127/0x280 block/blk-mq-sched.c:469
 blk_mq_submit_bio+0x524/0xe90 block/blk-mq.c:2262
 __submit_bio_noacct_mq block/blk-core.c:1014 [inline]
 submit_bio_noacct+0x6f2/0x7e0 block/blk-core.c:1047
 submit_bio+0x16d/0x2b0 block/blk-core.c:1090
 submit_bh_wbc+0x2f3/0x330 fs/buffer.c:3075
 submit_bh fs/buffer.c:3081 [inline]
 __sync_dirty_buffer+0x136/0x1e0 fs/buffer.c:3176
 sync_dirty_buffer+0x16/0x20 fs/buffer.c:3189
 ext4_write_inode+0x285/0x390 fs/ext4/inode.c:5236
 write_inode+0x8c/0x180 fs/fs-writeback.c:1320
 __writeback_single_inode+0x2a2/0x450 fs/fs-writeback.c:1525
 writeback_single_inode+0x177/0x590 fs/fs-writeback.c:1580
 sync_inode fs/fs-writeback.c:2624 [inline]
 sync_inode_metadata+0x57/0x80 fs/fs-writeback.c:2644
 ext4_fsync_nojournal fs/ext4/fsync.c:92 [inline]
 ext4_sync_file+0x359/0x670 fs/ext4/fsync.c:170
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2982 [inline]
 ext4_buffered_write_iter+0x39c/0x3f0 fs/ext4/file.c:277
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2114 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1325 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7681 Comm: syz-executor.1 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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