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BUG: KCSAN: data-race in bio_endio / blk_update_request

read-write to 0xffff88810b862b14 of 2 bytes by interrupt on cpu 0:
 bio_clear_flag include/linux/bio.h:263 [inline]
 blk_update_request+0x3a8/0xb00 block/blk-core.c:1461
 blk_mq_end_request+0x22/0x50 block/blk-mq.c:564
 end_cmd+0x80/0x140 drivers/block/null_blk/main.c:699
 null_complete_rq+0x18/0x20 drivers/block/null_blk/main.c:726
 blk_done_softirq+0x145/0x190 block/blk-mq.c:588
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:343
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:650
 smpboot_thread_fn+0x34f/0x520 kernel/smpboot.c:165
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88810b862b14 of 2 bytes by interrupt on cpu 1:
 bio_flagged include/linux/bio.h:253 [inline]
 bio_remaining_done block/bio.c:1390 [inline]
 bio_endio+0x3c/0x350 block/bio.c:1420
 req_bio_endio block/blk-core.c:264 [inline]
 blk_update_request+0x4e5/0xb00 block/blk-core.c:1462
 blk_mq_end_request+0x22/0x50 block/blk-mq.c:564
 end_cmd+0x80/0x140 drivers/block/null_blk/main.c:699
 null_complete_rq+0x18/0x20 drivers/block/null_blk/main.c:726
 blk_done_softirq+0x145/0x190 block/blk-mq.c:588
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:343
 run_ksoftirqd+0x13/0x20 kernel/softirq.c:650
 smpboot_thread_fn+0x34f/0x520 kernel/smpboot.c:165
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18 Comm: ksoftirqd/1 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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