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BUG: KCSAN: data-race in __blk_mq_sched_dispatch_requests / blk_mq_do_dispatch_sched

write to 0xffff8881295cd010 of 8 bytes by task 3256 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 0xffff8881295cd010 of 8 bytes by task 5040 on cpu 1:
 list_empty_careful include/linux/list.h:319 [inline]
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:144 [inline]
 blk_mq_do_dispatch_sched+0x17c/0x610 block/blk-mq-sched.c:205
 __blk_mq_sched_dispatch_requests+0x1fd/0x2a0 block/blk-mq-sched.c:316
 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_run_work_fn+0x3d/0x50 block/blk-mq.c:1803
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5040 Comm: kworker/1:1H Not tainted 5.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kblockd blk_mq_run_work_fn
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