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BUG: KCSAN: data-race in fprop_new_period / fprop_reflect_period_percpu

read-write to 0xffffffff86f020c0 of 4 bytes by interrupt on cpu 0:
 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
 replace_slot lib/radix-tree.c:826 [inline]
 __radix_tree_replace+0x172/0x1c0 lib/radix-tree.c:888
 radix_tree_iter_replace+0x33/0x40 lib/radix-tree.c:933
 idr_alloc_u32 lib/idr.c:52 [inline]
 idr_alloc_cyclic+0x1e4/0x2e0 lib/idr.c:125
 __kernfs_new_node+0xb3/0x330 fs/kernfs/dir.c:620
 kernfs_new_node+0x5b/0xd0 fs/kernfs/dir.c:676
 __kernfs_create_file+0x45/0x180 fs/kernfs/file.c:1047
 sysfs_add_file_mode_ns+0x10a/0x1d0 fs/sysfs/file.c:294
 create_files fs/sysfs/group.c:64 [inline]
 internal_create_group+0x2ed/0x830 fs/sysfs/group.c:148
 internal_create_groups fs/sysfs/group.c:188 [inline]
 sysfs_create_groups+0x3d/0xf0 fs/sysfs/group.c:214
 device_add_groups drivers/base/core.c:2573 [inline]
 device_add_attrs+0x69/0x400 drivers/base/core.c:2682
 device_add+0x4ef/0xb20 drivers/base/core.c:3430
 netdev_register_kobject+0xfa/0x230 net/core/net-sysfs.c:2015
 register_netdevice+0xafd/0xe10 net/core/dev.c:10045
 __ip_tunnel_create+0x1c5/0x260 net/ipv4/ip_tunnel.c:267
 ip_tunnel_init_net+0x18e/0x3d0 net/ipv4/ip_tunnel.c:1073
 vti_init_net+0x35/0xe0 net/ipv4/ip_vti.c:504
 ops_init+0x215/0x2d0 net/core/net_namespace.c:135
 setup_net+0x39b/0x8e0 net/core/net_namespace.c:333
 copy_net_ns+0x29f/0x450 net/core/net_namespace.c:483
 create_new_namespaces+0x22c/0x450 kernel/nsproxy.c:110
 copy_namespaces+0x149/0x1a0 kernel/nsproxy.c:179
 copy_process+0xda6/0x2090 kernel/fork.c:2269
 kernel_clone+0x166/0x550 kernel/fork.c:2681
 __do_sys_clone kernel/fork.c:2822 [inline]
 __se_sys_clone kernel/fork.c:2806 [inline]
 __x64_sys_clone+0xc3/0xf0 kernel/fork.c:2806
 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 0xffffffff86f020c0 of 4 bytes by task 16533 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+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:308

value changed: 0x00000149 -> 0x0000014a

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 16533 Comm: kworker/u4:20 Not tainted 6.2.0-rc5-syzkaller-00047-g7c46948a6e9c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/12/2023
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
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