syzbot

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

read-write to 0xffffffff86f40070 of 4 bytes by interrupt on cpu 1:
 fprop_new_period+0xaa/0xe0 lib/flex_proportions.c:79
 writeout_period+0x59/0xe0 mm/page-writeback.c:613
 call_timer_fn+0x35/0x290 kernel/time/timer.c:1700
 expire_timers kernel/time/timer.c:1751 [inline]
 __run_timers+0x46c/0x650 kernel/time/timer.c:2022
 run_timer_softirq+0x31/0x40 kernel/time/timer.c:2037
 __do_softirq+0xc1/0x265 kernel/softirq.c:571
 invoke_softirq kernel/softirq.c:445 [inline]
 __irq_exit_rcu+0x57/0xa0 kernel/softirq.c:650
 sysvec_apic_timer_interrupt+0x6d/0x80 arch/x86/kernel/apic/apic.c:1107
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
 __preempt_count_dec_and_test arch/x86/include/asm/preempt.h:95 [inline]
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock_irqrestore+0x3d/0x50 kernel/locking/spinlock.c:194
 spin_unlock_irqrestore include/linux/spinlock.h:405 [inline]
 __folio_start_writeback+0x36b/0x4b0 mm/page-writeback.c:3091
 set_page_writeback+0x46/0xf0 mm/folio-compat.c:51
 ext4_bio_write_page+0x61a/0xcf0 fs/ext4/page-io.c:560
 mpage_submit_page fs/ext4/inode.c:2129 [inline]
 mpage_map_and_submit_buffers fs/ext4/inode.c:2374 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2513 [inline]
 ext4_do_writepages+0x138c/0x2140 fs/ext4/inode.c:2876
 ext4_writepages+0x130/0x260 fs/ext4/inode.c:2964
 do_writepages+0x1c5/0x340 mm/page-writeback.c:2551
 __writeback_single_inode+0x91/0x860 fs/fs-writeback.c:1600
 writeback_sb_inodes+0x515/0xaa0 fs/fs-writeback.c:1891
 __writeback_inodes_wb+0x9a/0x1a0 fs/fs-writeback.c:1962
 wb_writeback+0x24d/0x6c0 fs/fs-writeback.c:2067
 wb_check_start_all fs/fs-writeback.c:2189 [inline]
 wb_do_writeback fs/fs-writeback.c:2215 [inline]
 wb_workfn+0x4ea/0x8d0 fs/fs-writeback.c:2248
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2390
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2537
 kthread+0x1a6/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

read to 0xffffffff86f40070 of 4 bytes by task 16605 on cpu 0:
 fprop_reflect_period_percpu+0x22/0x1a0 lib/flex_proportions.c:188
 __fprop_add_percpu lib/flex_proportions.c:219 [inline]
 __fprop_add_percpu_max+0x58/0x180 lib/flex_proportions.c:277
 wb_domain_writeout_add mm/page-writeback.c:560 [inline]
 __wb_writeout_add+0x7e/0x1d0 mm/page-writeback.c:584
 __folio_end_writeback+0x26f/0x500 mm/page-writeback.c:3023
 folio_end_writeback+0x5b/0x150 mm/filemap.c:1618
 end_page_writeback+0x44/0xf0 mm/folio-compat.c:27
 ext4_finish_bio+0x3d8/0x4d0 fs/ext4/page-io.c:145
 ext4_release_io_end+0x8c/0x1e0 fs/ext4/page-io.c:160
 ext4_end_io_end fs/ext4/page-io.c:194 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:259 [inline]
 ext4_end_io_rsv_work+0x2d3/0x360 fs/ext4/page-io.c:273
 process_one_work+0x3e6/0x750 kernel/workqueue.c:2390
 worker_thread+0x5f2/0xa10 kernel/workqueue.c:2537
 kthread+0x1a6/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

value changed: 0x0000038b -> 0x0000038c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16605 Comm: kworker/u4:3 Not tainted 6.3.0-rc5-syzkaller-00022-g76f598ba7d8e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================