syzbot

==================================================================
BUG: KCSAN: data-race in fprop_new_period / fprop_reflect_period_percpu

write to 0xffffffff8455f308 of 4 bytes by interrupt on cpu 0:
 fprop_new_period+0x100/0x180 lib/flex_proportions.c:83
 writeout_period+0x55/0xe0 mm/page-writeback.c:628
 call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1431
 expire_timers+0x135/0x250 kernel/time/timer.c:1476
 __run_timers+0x358/0x420 kernel/time/timer.c:1745
 run_timer_softirq+0x2d/0x30 kernel/time/timer.c:1760
 __do_softirq+0x12c/0x275 kernel/softirq.c:559
 invoke_softirq kernel/softirq.c:433 [inline]
 __irq_exit_rcu+0xa5/0xb0 kernel/softirq.c:637
 sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:647
 write_comp_data kernel/kcov.c:240 [inline]
 __sanitizer_cov_trace_const_cmp2+0x90/0xa0 kernel/kcov.c:277
 blk_mq_submit_bio+0x5fe/0xe90 block/blk-mq.c:2253
 __submit_bio_noacct_mq block/blk-core.c:1014 [inline]
 submit_bio_noacct+0x6f2/0x7e0 block/blk-core.c:1047
 submit_bio+0x16d/0x2b0 block/blk-core.c:1090
 submit_bh_wbc+0x2f3/0x330 fs/buffer.c:3075
 __block_write_full_page+0x648/0xa10 fs/buffer.c:1830
 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
 __writeback_single_inode+0x80/0x450 fs/fs-writeback.c:1467
 writeback_sb_inodes+0x564/0xf10 fs/fs-writeback.c:1732
 __writeback_inodes_wb fs/fs-writeback.c:1801 [inline]
 wb_writeback+0x327/0x700 fs/fs-writeback.c:1907
 wb_check_start_all fs/fs-writeback.c:2031 [inline]
 wb_do_writeback+0x330/0x510 fs/fs-writeback.c:2057
 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 0xffffffff8455f308 of 4 bytes by task 8 on cpu 1:
 fprop_reflect_period_percpu+0x22/0x1a0 lib/flex_proportions.c:192
 __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
 ext4_finish_bio+0x3e2/0x430 fs/ext4/page-io.c:143
 ext4_release_io_end+0x98/0x200 fs/ext4/page-io.c:158
 ext4_end_io_end fs/ext4/page-io.c:192 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:257 [inline]
 ext4_end_io_rsv_work+0x306/0x360 fs/ext4/page-io.c:271
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================