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BUG: KCSAN: data-race in percpu_counter_add_batch / wb_over_bg_thresh

write to 0xffff88812aba24e0 of 8 bytes by task 9260 on cpu 0:
 percpu_counter_add_batch+0xca/0x150 lib/percpu_counter.c:91
 __add_wb_stat include/linux/backing-dev.h:73 [inline]
 inc_wb_stat include/linux/backing-dev.h:78 [inline]
 account_page_dirtied+0x1f1/0x4a0 mm/page-writeback.c:2427
 __set_page_dirty+0x8a/0x270 fs/buffer.c:623
 mark_buffer_dirty+0x27f/0x2c0 fs/buffer.c:1152
 __block_commit_write.isra.0+0x11f/0x170 fs/buffer.c:2081
 block_commit_write fs/buffer.c:2473 [inline]
 block_page_mkwrite+0x226/0x230 fs/buffer.c:2522
 ext4_page_mkwrite+0x5ca/0xe50 fs/ext4/inode.c:5902
 do_page_mkwrite+0x100/0x210 mm/memory.c:2276
 do_shared_fault mm/memory.c:3650 [inline]
 do_fault mm/memory.c:3718 [inline]
 handle_pte_fault mm/memory.c:3945 [inline]
 __handle_mm_fault+0x1e45/0x2e00 mm/memory.c:4075
 handle_mm_fault+0x21b/0x530 mm/memory.c:4112
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x456/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

read to 0xffff88812aba24e0 of 8 bytes by task 8108 on cpu 1:
 wb_stat include/linux/backing-dev.h:88 [inline]
 wb_over_bg_thresh+0x247/0x490 mm/page-writeback.c:1948
 wb_check_background_flush fs/fs-writeback.c:1952 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x3b3/0x970 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8108 Comm: kworker/u4:2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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