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BUG: KCSAN: data-race in fprop_reflect_period_percpu / fprop_reflect_period_percpu

write to 0xffff888101a2b1c8 of 4 bytes by task 26966 on cpu 1:
 fprop_reflect_period_percpu+0x17c/0x1a0 lib/flex_proportions.c:215
 fprop_fraction_percpu+0xaa/0x170 lib/flex_proportions.c:236
 __wb_calc_thresh mm/page-writeback.c:769 [inline]
 wb_calc_thresh mm/page-writeback.c:789 [inline]
 wb_over_bg_thresh+0x17a/0x270 mm/page-writeback.c:1961
 wb_check_background_flush fs/fs-writeback.c:1965 [inline]
 wb_do_writeback+0x493/0x510 fs/fs-writeback.c:2063
 wb_workfn+0xc8/0x520 fs/fs-writeback.c:2091
 process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
 worker_thread+0x636/0xae0 kernel/workqueue.c:2422
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888101a2b1c8 of 4 bytes by task 1769 on cpu 0:
 fprop_reflect_period_percpu+0x32/0x1a0 lib/flex_proportions.c:196
 __fprop_inc_percpu lib/flex_proportions.c:222 [inline]
 __fprop_inc_percpu_max+0x3f/0x1f0 lib/flex_proportions.c:271
 wb_domain_writeout_inc mm/page-writeback.c:575 [inline]
 __wb_writeout_inc mm/page-writeback.c:599 [inline]
 test_clear_page_writeback+0x37b/0x560 mm/page-writeback.c:2742
 end_page_writeback+0xd7/0x1b0 mm/filemap.c:1548
 __block_write_full_page+0x692/0xa10 fs/buffer.c:1846
 block_write_full_page+0x240/0x260 fs/buffer.c:3001
 blkdev_writepage+0x20/0x30 fs/block_dev.c:639
 __writepage+0x32/0xc0 mm/page-writeback.c:2311
 write_cache_pages+0x4d7/0x810 mm/page-writeback.c:2246
 generic_writepages+0x64/0xa0 mm/page-writeback.c:2337
 blkdev_writepages+0x19/0x20 fs/block_dev.c:1753
 do_writepages+0x7b/0x150 mm/page-writeback.c:2352
 __filemap_fdatawrite_range mm/filemap.c:413 [inline]
 __filemap_fdatawrite mm/filemap.c:421 [inline]
 filemap_flush+0x132/0x160 mm/filemap.c:448
 __sync_blockdev+0x69/0x70 fs/block_dev.c:525
 __sync_filesystem fs/sync.c:40 [inline]
 sync_filesystem+0xcb/0x160 fs/sync.c:64
 generic_shutdown_super+0x42/0x230 fs/super.c:448
 kill_block_super+0x4a/0x90 fs/super.c:1395
 deactivate_locked_super+0x65/0xd0 fs/super.c:335
 deactivate_super+0x85/0x90 fs/super.c:366
 cleanup_mnt+0x267/0x2d0 fs/namespace.c:1136
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1143
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000013d -> 0x0000013e

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1769 Comm: syz-executor.3 Not tainted 5.13.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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