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BUG: KCSAN: data-race in bio_endio / blk_update_request

write to 0xffff8881241b7f14 of 2 bytes by interrupt on cpu 0:
 bio_clear_flag include/linux/bio.h:244 [inline]
 blk_update_request+0x35a/0x7a0 block/blk-core.c:1467
 blk_mq_end_request+0x4e/0x2f0 block/blk-mq.c:546
 end_cmd drivers/block/null_blk_main.c:648 [inline]
 end_cmd+0xa4/0x190 drivers/block/null_blk_main.c:642
 null_complete_rq+0x1f/0x30 drivers/block/null_blk_main.c:675
 blk_done_softirq+0x1e6/0x250 block/blk-softirq.c:37
 __do_softirq+0x118/0x34a kernel/softirq.c:292
 run_ksoftirqd+0x41/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x374/0x4a0 kernel/smpboot.c:165
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8881241b7f14 of 2 bytes by interrupt on cpu 1:
 bio_remaining_done block/bio.c:1811 [inline]
 bio_endio+0x3c/0x3e0 block/bio.c:1841
 req_bio_endio block/blk-core.c:245 [inline]
 blk_update_request+0x418/0x7a0 block/blk-core.c:1468
 blk_mq_end_request+0x4e/0x2f0 block/blk-mq.c:546
 end_cmd drivers/block/null_blk_main.c:648 [inline]
 end_cmd+0xa4/0x190 drivers/block/null_blk_main.c:642
 null_complete_rq+0x1f/0x30 drivers/block/null_blk_main.c:675
 blk_done_softirq+0x1e6/0x250 block/blk-softirq.c:37
 __do_softirq+0x118/0x34a kernel/softirq.c:292
 run_ksoftirqd+0x41/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x374/0x4a0 kernel/smpboot.c:165
 kthread+0x1cb/0x1f0 kernel/kthread.c:255
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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