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BUG: KCSAN: data-race in __blk_mq_sched_dispatch_requests / blk_mq_run_hw_queue

write to 0xffff8881024b8010 of 8 bytes by task 2048 on cpu 1:
 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:289
 blk_mq_sched_dispatch_requests+0x9f/0x110 block/blk-mq-sched.c:341
 __blk_mq_run_hw_queue block/blk-mq.c:1515 [inline]
 __blk_mq_delay_run_hw_queue+0x207/0x420 block/blk-mq.c:1592
 blk_mq_run_hw_queue+0x231/0x260 block/blk-mq.c:1645
 blk_mq_run_hw_queues block/blk-mq.c:1663 [inline]
 blk_mq_requeue_work+0x423/0x490 block/blk-mq.c:824
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff8881024b8010 of 8 bytes by task 3752 on cpu 0:
 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:1641
 blk_mq_sched_insert_requests+0x144/0x210 block/blk-mq-sched.c:501
 blk_mq_flush_plug_list+0x2f5/0x400 block/blk-mq.c:1915
 blk_flush_plug_list+0x235/0x260 block/blk-core.c:1755
 blk_finish_plug+0x44/0x60 block/blk-core.c:1772
 ext4_writepages+0x18dd/0x1e70 fs/ext4/inode.c:2852
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range+0x19d/0x1d0 mm/filemap.c:422
 file_write_and_wait_range+0x9f/0x120 mm/filemap.c:761
 ext4_sync_file+0x105/0x6e0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x107/0x120 fs/sync.c:200
 generic_write_sync include/linux/fs.h:2737 [inline]
 ext4_buffered_write_iter+0x38f/0x3e0 fs/ext4/file.c:278
 ext4_file_write_iter+0x47a/0x1060 fs/ext4/file.c:503
 call_write_iter include/linux/fs.h:1901 [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+0x41a/0x770 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5e0/0xcf0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1304
 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: 0 PID: 3752 Comm: syz-executor.0 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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