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BUG: KCSAN: data-race in __blk_mq_free_request / bt_for_each

write to 0xffff888101b34ed0 of 8 bytes by interrupt on cpu 1:
 __blk_mq_free_request+0xcd/0x180 block/blk-mq.c:498
 blk_mq_free_request+0x2c8/0x330 block/blk-mq.c:534
 __blk_mq_end_request+0x214/0x230 block/blk-mq.c:558
 blk_mq_end_request+0x37/0x50 block/blk-mq.c:567
 lo_complete_rq+0xca/0x170 drivers/block/loop.c:498
 blk_complete_reqs block/blk-mq.c:577 [inline]
 blk_done_softirq+0x69/0x90 block/blk-mq.c:582
 __do_softirq+0x12c/0x275 kernel/softirq.c:559
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:921
 smpboot_thread_fn+0x2a1/0x3f0 kernel/smpboot.c:165
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888101b34ed0 of 8 bytes by task 702 on cpu 0:
 bt_iter block/blk-mq-tag.c:218 [inline]
 __sbitmap_for_each_set include/linux/sbitmap.h:263 [inline]
 sbitmap_for_each_set include/linux/sbitmap.h:284 [inline]
 bt_for_each+0x229/0x320 block/blk-mq-tag.c:247
 blk_mq_queue_tag_busy_iter+0x19f/0x290 block/blk-mq-tag.c:436
 blk_mq_timeout_work+0x99/0x2d0 block/blk-mq.c:977
 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: 0xffff888100dc7800 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 702 Comm: kworker/0:1H Not tainted 5.13.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kblockd blk_mq_timeout_work
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