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

read-write to 0xffffffff86eeace0 of 4 bytes by interrupt on cpu 0:
 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:553
 invoke_softirq kernel/softirq.c:427 [inline]
 __irq_exit_rcu kernel/softirq.c:632 [inline]
 irq_exit_rcu+0x3b/0x90 kernel/softirq.c:644
 sysvec_apic_timer_interrupt+0x6d/0x80 arch/x86/kernel/apic/apic.c:1074
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:645
 is_atomic kernel/kcsan/core.c:264 [inline]
 should_watch kernel/kcsan/core.c:277 [inline]
 check_access kernel/kcsan/core.c:752 [inline]
 __tsan_unaligned_write8+0x146/0x180 kernel/kcsan/core.c:1025
 __kernfs_create_file+0x69/0x180 fs/kernfs/file.c:1052
 sysfs_add_file_mode_ns+0x136/0x1b0 fs/sysfs/file.c:294
 sysfs_merge_group+0xfd/0x1d0 fs/sysfs/group.c:346
 dpm_sysfs_add+0xae/0x1e0 drivers/base/power/sysfs.c:707
 device_add+0x473/0x8b0 drivers/base/core.c:3584
 netdev_register_kobject+0xfc/0x230 net/core/net-sysfs.c:2044
 register_netdevice+0x650/0xb20 net/core/dev.c:10136
 __ip_tunnel_create+0x1c5/0x260 net/ipv4/ip_tunnel.c:267
 ip_tunnel_init_net+0x183/0x3c0 net/ipv4/ip_tunnel.c:1091
 ipip_init_net+0x35/0x40 net/ipv4/ipip.c:592
 ops_init+0x1fc/0x2c0 net/core/net_namespace.c:136
 setup_net+0x2cd/0x710 net/core/net_namespace.c:339
 copy_net_ns+0x384/0x520 net/core/net_namespace.c:491
 create_new_namespaces+0x228/0x430 kernel/nsproxy.c:110
 copy_namespaces+0x1a9/0x200 kernel/nsproxy.c:179
 copy_process+0x102f/0x2180 kernel/fork.c:2504
 kernel_clone+0x169/0x560 kernel/fork.c:2909
 __do_sys_clone3 kernel/fork.c:3210 [inline]
 __se_sys_clone3+0x1b5/0x1f0 kernel/fork.c:3194
 __x64_sys_clone3+0x31/0x40 kernel/fork.c:3194
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffffff86eeace0 of 4 bytes by task 19403 on cpu 1:
 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+0x264/0x4f0 mm/page-writeback.c:2964
 folio_end_writeback+0x5b/0x150 mm/filemap.c:1613
 ext4_finish_bio+0x45c/0x8c0 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 kernel/workqueue.c:2630 [inline]
 process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703
 worker_thread+0x525/0x730 kernel/workqueue.c:2784
 kthread+0x1d7/0x210 kernel/kthread.c:388
 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304

value changed: 0x000000c1 -> 0x000000c2

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19403 Comm: kworker/u4:0 Not tainted 6.6.0-rc4-syzkaller-00016-g5e62ed3b1c8a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
==================================================================