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BUG: KCSAN: data-race in wbt_inflight_cb / wbt_wait

write to 0xffff88812aedd340 of 8 bytes by task 16315 on cpu 1:
 wb_timestamp block/blk-wbt.c:89 [inline]
 wbt_wait+0x12b/0x2b0 block/blk-wbt.c:579
 __rq_qos_throttle+0x39/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_submit_bio+0x244/0x1130 block/blk-mq.c:2168
 __submit_bio_noacct_mq block/blk-core.c:1180 [inline]
 submit_bio_noacct+0x772/0x950 block/blk-core.c:1213
 submit_bio+0x200/0x370 block/blk-core.c:1283
 mpage_bio_submit fs/mpage.c:66 [inline]
 mpage_readahead+0x2fa/0x340 fs/mpage.c:395
 blkdev_readahead+0x18/0x20 fs/block_dev.c:608
 read_pages+0x9c/0x700 mm/readahead.c:130
 page_cache_readahead_unbounded+0x41a/0x470 mm/readahead.c:244
 __do_page_cache_readahead mm/readahead.c:273 [inline]
 force_page_cache_readahead+0x1ec/0x220 mm/readahead.c:303
 page_cache_sync_readahead+0x191/0x1a0 mm/readahead.c:580
 generic_file_buffered_read+0x2ec/0x1f60 mm/filemap.c:2101
 generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2405
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1927
 call_read_iter include/linux/fs.h:1876 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x57a/0x5e0 fs/read_write.c:481
 ksys_read+0xce/0x180 fs/read_write.c:607
 __do_sys_read fs/read_write.c:617 [inline]
 __se_sys_read fs/read_write.c:615 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:615
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812aedd340 of 8 bytes by task 16362 on cpu 0:
 close_io block/blk-wbt.c:444 [inline]
 get_limit block/blk-wbt.c:474 [inline]
 wbt_inflight_cb+0x19a/0x220 block/blk-wbt.c:495
 rq_qos_wait+0xac/0x220 block/blk-rq-qos.c:266
 __wbt_wait block/blk-wbt.c:518 [inline]
 wbt_wait+0x1bb/0x2b0 block/blk-wbt.c:583
 __rq_qos_throttle+0x39/0x70 block/blk-rq-qos.c:72
 rq_qos_throttle block/blk-rq-qos.h:182 [inline]
 blk_mq_submit_bio+0x244/0x1130 block/blk-mq.c:2168
 __submit_bio_noacct_mq block/blk-core.c:1180 [inline]
 submit_bio_noacct+0x772/0x950 block/blk-core.c:1213
 submit_bio+0x200/0x370 block/blk-core.c:1283
 submit_bh_wbc+0x397/0x3d0 fs/buffer.c:3070
 __block_write_full_page+0x618/0x9c0 fs/buffer.c:1810
 block_write_full_page+0x172/0x1b0 fs/buffer.c:2996
 fat_writepage+0x20/0x30 fs/fat/inode.c:199
 writeout mm/migrate.c:892 [inline]
 fallback_migrate_page mm/migrate.c:916 [inline]
 move_to_new_page+0x305/0x6c0 mm/migrate.c:967
 __unmap_and_move+0x3f4/0x6a0 mm/migrate.c:1130
 unmap_and_move+0x130/0x870 mm/migrate.c:1196
 migrate_pages+0x213/0xc20 mm/migrate.c:1457
 do_mbind mm/mempolicy.c:1354 [inline]
 kernel_mbind+0xe88/0x1010 mm/mempolicy.c:1475
 __do_sys_mbind mm/mempolicy.c:1482 [inline]
 __se_sys_mbind mm/mempolicy.c:1478 [inline]
 __x64_sys_mbind+0x74/0x80 mm/mempolicy.c:1478
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16362 Comm: syz-executor.3 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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