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BUG: KCSAN: data-race in __wb_update_bandwidth / bdi_split_work_to_wbs

write to 0xffff888055ce2128 of 8 bytes by task 7 on cpu 0:
 wb_update_write_bandwidth mm/page-writeback.c:1130 [inline]
 __wb_update_bandwidth+0x28a/0x3d0 mm/page-writeback.c:1387
 wb_update_bandwidth+0x93/0xc0 mm/page-writeback.c:1399
 wb_writeback+0x21d/0x6a0 fs/fs-writeback.c:1897
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x215/0x970 fs/fs-writeback.c:2078
 process_one_work+0x424/0x930 kernel/workqueue.c:2268
 worker_thread+0x9a/0x7e0 kernel/workqueue.c:2414
 kthread+0x203/0x230 kernel/kthread.c:268
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff888055ce2128 of 8 bytes by task 9420 on cpu 1:
 bdi_split_work_to_wbs+0x279/0x630 fs/fs-writeback.c:869
 __writeback_inodes_sb_nr+0x194/0x1e0 fs/fs-writeback.c:2468
 writeback_inodes_sb_nr fs/fs-writeback.c:2486 [inline]
 writeback_inodes_sb+0x2d/0x40 fs/fs-writeback.c:2501
 __sync_filesystem fs/sync.c:36 [inline]
 sync_filesystem+0xbf/0x1a0 fs/sync.c:64
 ovl_sync_fs+0x89/0xa0 fs/overlayfs/super.c:277
 __sync_filesystem fs/sync.c:39 [inline]
 sync_filesystem fs/sync.c:67 [inline]
 sync_filesystem+0x15d/0x1a0 fs/sync.c:48
 generic_shutdown_super+0x68/0x270 fs/super.c:448
 kill_anon_super+0x28/0x50 fs/super.c:1108
 deactivate_locked_super+0x5d/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27a/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1c/0x30 fs/namespace.c:1109
 task_work_run+0xba/0x120 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:165
 prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x38b/0x3b0 arch/x86/entry/common.c:305
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9420 Comm: syz-executor.4 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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