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BUG: KCSAN: data-race in wbt_inflight_cb / wbt_wait

write to 0xffff88812a4b0940 of 8 bytes by task 8465 on cpu 1:
 wb_timestamp block/blk-wbt.c:89 [inline]
 wb_timestamp block/blk-wbt.c:83 [inline]
 wbt_wait+0x22a/0x260 block/blk-wbt.c:587
 __rq_qos_throttle+0x42/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_make_request+0x297/0xf60 block/blk-mq.c:1984
 generic_make_request block/blk-core.c:1069 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1011
 submit_bio+0x8f/0x3a0 block/blk-core.c:1195
 mpage_bio_submit fs/mpage.c:66 [inline]
 mpage_readpages+0x325/0x370 fs/mpage.c:410
 blkdev_readpages+0x32/0x50 fs/block_dev.c:620
 read_pages+0xa2/0x2d0 mm/readahead.c:126
 __do_page_cache_readahead+0x358/0x380 mm/readahead.c:212
 force_page_cache_readahead+0x12c/0x1e0 mm/readahead.c:243
 page_cache_sync_readahead+0x1d1/0x1e0 mm/readahead.c:522
 generic_file_buffered_read mm/filemap.c:2029 [inline]
 generic_file_read_iter+0xeae/0x1490 mm/filemap.c:2302
 blkdev_read_iter+0xae/0xe0 fs/block_dev.c:2039
 call_read_iter include/linux/fs.h:1895 [inline]
 new_sync_read+0x306/0x450 fs/read_write.c:414
 __vfs_read+0x9e/0xb0 fs/read_write.c:427
 vfs_read fs/read_write.c:461 [inline]
 vfs_read+0x13e/0x2b0 fs/read_write.c:446
 ksys_read+0xc5/0x1a0 fs/read_write.c:587
 __do_sys_read fs/read_write.c:597 [inline]
 __se_sys_read fs/read_write.c:595 [inline]
 __x64_sys_read+0x49/0x60 fs/read_write.c:595
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a4b0940 of 8 bytes by task 8455 on cpu 0:
 get_limit block/blk-wbt.c:482 [inline]
 wbt_inflight_cb+0x1a8/0x220 block/blk-wbt.c:503
 rq_qos_wait+0x26b/0x300 block/blk-rq-qos.c:266
 __wbt_wait block/blk-wbt.c:526 [inline]
 wbt_wait+0x15f/0x260 block/blk-wbt.c:591
 __rq_qos_throttle+0x42/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_make_request+0x297/0xf60 block/blk-mq.c:1984
 generic_make_request block/blk-core.c:1069 [inline]
 generic_make_request+0x196/0x700 block/blk-core.c:1011
 submit_bio+0x8f/0x3a0 block/blk-core.c:1195
 blk_next_bio+0x4f/0x70 block/blk-lib.c:19
 __blkdev_issue_zero_pages+0x106/0x2f0 block/blk-lib.c:284
 blkdev_issue_zeroout+0x32d/0x360 block/blk-lib.c:378
 blkdev_fallocate+0x25f/0x2e0 fs/block_dev.c:2118
 vfs_fallocate+0x3b1/0x650 fs/open.c:309
 ksys_fallocate+0x5b/0xa0 fs/open.c:332
 __do_sys_fallocate fs/open.c:340 [inline]
 __se_sys_fallocate fs/open.c:338 [inline]
 __x64_sys_fallocate+0x59/0x70 fs/open.c:338
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8455 Comm: syz-executor.0 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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