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BUG: KCSAN: data-race in fprop_new_period / fprop_reflect_period_percpu

read-write to 0xffffffff870f16b0 of 4 bytes by interrupt on cpu 1:
 fprop_new_period+0xa6/0xd0 lib/flex_proportions.c:79
 writeout_period+0x55/0xe0 mm/page-writeback.c:613
 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1700
 expire_timers+0x11f/0x260 kernel/time/timer.c:1751
 __run_timers+0x350/0x400 kernel/time/timer.c:2022
 run_timer_softirq+0x56/0x60 kernel/time/timer.c:2037
 __do_softirq+0xf2/0x2c7 kernel/softirq.c:571
 __irq_exit_rcu kernel/softirq.c:650 [inline]
 irq_exit_rcu+0x41/0x70 kernel/softirq.c:662
 sysvec_apic_timer_interrupt+0x8d/0xb0 arch/x86/kernel/apic/apic.c:1107
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:649
 kcsan_setup_watchpoint+0x3e9/0x3f0 kernel/kcsan/core.c:696
 insert_entry fs/proc/proc_sysctl.c:153 [inline]
 insert_header+0x56d/0x8e0 fs/proc/proc_sysctl.c:252
 __register_sysctl_table+0xc77/0xce0 fs/proc/proc_sysctl.c:1372
 register_net_sysctl+0x1b1/0x1c0 net/sysctl_net.c:169
 neigh_sysctl_register+0x342/0x3c0 net/core/neighbour.c:3854
 devinet_sysctl_register+0x75/0x130 net/ipv4/devinet.c:2624
 inetdev_init+0x1f5/0x370 net/ipv4/devinet.c:286
 inetdev_event+0x175/0xae0 net/ipv4/devinet.c:1535
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0x53/0xb0 kernel/notifier.c:455
 call_netdevice_notifiers_info net/core/dev.c:1944 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:1982 [inline]
 call_netdevice_notifiers+0xb8/0x120 net/core/dev.c:1996
 register_netdevice+0xca3/0xe10 net/core/dev.c:10078
 tun_set_iff+0x5e2/0x820 drivers/net/tun.c:2824
 __tun_chr_ioctl+0x5ed/0x1740 drivers/net/tun.c:3092
 tun_chr_ioctl+0x23/0x30 drivers/net/tun.c:3377
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffffff870f16b0 of 4 bytes by task 8980 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+0x54/0x180 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+0x246/0x4d0 mm/page-writeback.c:3044
 folio_end_writeback+0x57/0x130 mm/filemap.c:1614
 end_page_writeback+0x3b/0xe0 mm/folio-compat.c:26
 ext4_finish_bio+0x421/0x520 fs/ext4/page-io.c:145
 ext4_release_io_end+0x98/0x200 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+0x319/0x3a0 fs/ext4/page-io.c:273
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

value changed: 0x00000191 -> 0x00000192

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8980 Comm: kworker/u4:2 Not tainted 6.1.0-syzkaller-09941-ge2ca6ba6ba01-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
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