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BUG: KCSAN: data-race in __wb_update_bandwidth / bdi_split_work_to_wbs

write to 0xffff8880a7480528 of 8 bytes by task 2647 on cpu 1:
 wb_update_write_bandwidth mm/page-writeback.c:1130 [inline]
 __wb_update_bandwidth+0x277/0x3c0 mm/page-writeback.c:1387
 wb_update_bandwidth+0x90/0xc0 mm/page-writeback.c:1399
 wb_writeback+0x21d/0x6a0 fs/fs-writeback.c:1897
 wb_check_start_all fs/fs-writeback.c:2018 [inline]
 wb_do_writeback fs/fs-writeback.c:2044 [inline]
 wb_workfn+0x748/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880a7480528 of 8 bytes by task 15516 on cpu 0:
 bdi_split_work_to_wbs+0x2ca/0x6b0 fs/fs-writeback.c:869
 sync_inodes_sb+0x17a/0x530 fs/fs-writeback.c:2554
 sync_inodes_one_sb+0x53/0x70 fs/sync.c:74
 iterate_supers+0x120/0x220 fs/super.c:692
 ksys_sync+0x5e/0xf0 fs/sync.c:113
 __ia32_sys_sync+0x17/0x20 fs/sync.c:124
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15516 Comm: syz-executor.1 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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