==================================================================
BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

write to 0xffff888129789940 of 8 bytes by task 21 on cpu 1:
 percpu_counter_add_batch+0xbd/0x130 lib/percpu_counter.c:91
 __add_wb_stat+0x4c/0x60 include/linux/backing-dev.h:70
 inc_wb_stat include/linux/backing-dev.h:75 [inline]
 __wb_writeout_inc+0x27/0x1a0 mm/page-writeback.c:598
 test_clear_page_writeback+0x2ef/0x480 mm/page-writeback.c:2745
 end_page_writeback+0xa7/0x110 mm/filemap.c:1369
 ext4_finish_bio+0x429/0x490 fs/ext4/page-io.c:146
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:161
 ext4_end_io_end fs/ext4/page-io.c:195 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:260 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:274
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888129789940 of 8 bytes by task 397 on cpu 0:
 percpu_counter_read include/linux/percpu_counter.h:72 [inline]
 __wb_update_bandwidth+0xa7/0x5d0 mm/page-writeback.c:1359
 wb_update_bandwidth+0x59/0x80 mm/page-writeback.c:1393
 wb_writeback+0x2f3/0x730 fs/fs-writeback.c:1897
 wb_do_writeback+0x108/0x610 fs/fs-writeback.c:2037
 wb_workfn+0xc8/0x460 fs/fs-writeback.c:2078
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 397 Comm: kworker/u4:3 Not tainted 5.9.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
==================================================================