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BUG: KCSAN: data-race in kthread_insert_work / kthread_worker_fn

write to 0xffff8881019e5540 of 8 bytes by task 27326 on cpu 0:
 kthread_worker_fn+0x6d/0x4d0 kernel/kthread.c:726
 loop_kthread_worker_fn+0x3e/0x50 drivers/block/loop.c:933
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8881019e5540 of 8 bytes by task 705 on cpu 1:
 kthread_insert_work+0xe4/0x1a0 kernel/kthread.c:912
 kthread_queue_work+0x73/0x90 kernel/kthread.c:936
 loop_queue_rq+0x10d/0x120 drivers/block/loop.c:2029
 blk_mq_dispatch_rq_list+0x628/0x10b0 block/blk-mq.c:1379
 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:191 [inline]
 blk_mq_do_dispatch_sched+0x3cb/0x660 block/blk-mq-sched.c:204
 __blk_mq_sched_dispatch_requests+0x21e/0x2c0 block/blk-mq-sched.c:320
 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_run_work_fn+0x3d/0x50 block/blk-mq.c:1831
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

value changed: 0x0000000000000000 -> 0xffff88812b9c6040

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 705 Comm: kworker/1:1H Not tainted 5.13.0-rc5-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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