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BUG: KCSAN: data-race in fprop_new_period / fprop_reflect_period_percpu

read-write to 0xffffffff86eff0c0 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
 EXT4_SB fs/ext4/ext4.h:1769 [inline]
 ext4_get_groups_count fs/ext4/ext4.h:3345 [inline]
 ext4_get_group_desc+0x29/0x190 fs/ext4/balloc.c:270
 __ext4_get_inode_loc+0x114/0x8e0 fs/ext4/inode.c:4544
 ext4_get_inode_loc fs/ext4/inode.c:4693 [inline]
 ext4_reserve_inode_write+0xac/0x1f0 fs/ext4/inode.c:5896
 __ext4_mark_inode_dirty+0x85/0x410 fs/ext4/inode.c:6073
 ext4_dirty_inode+0x8d/0xb0 fs/ext4/inode.c:6110
 __mark_inode_dirty+0x15b/0x730 fs/fs-writeback.c:2419
 mark_inode_dirty include/linux/fs.h:2462 [inline]
 dquot_alloc_space include/linux/quotaops.h:320 [inline]
 dquot_alloc_block include/linux/quotaops.h:337 [inline]
 ext4_mb_new_blocks+0xcef/0x1000 fs/ext4/mballoc.c:5571
 ext4_ext_map_blocks+0xd7d/0x1bf0 fs/ext4/extents.c:4286
 ext4_map_blocks+0x72d/0x1040 fs/ext4/inode.c:651
 _ext4_get_block+0x105/0x290 fs/ext4/inode.c:808
 ext4_get_block_unwritten+0x26/0x30 fs/ext4/inode.c:839
 __block_write_begin_int+0x33d/0xc50 fs/buffer.c:1991
 __block_write_begin+0x55/0x100 fs/buffer.c:2041
 ext4_write_begin+0x49c/0xff0
 ext4_da_write_begin+0x1ce/0x5f0 fs/ext4/inode.c:3058
 generic_perform_write+0x1d4/0x3f0 mm/filemap.c:3772
 ext4_buffered_write_iter+0x235/0x3e0 fs/ext4/file.c:285
 ext4_file_write_iter+0x2bb/0x11b0
 __kernel_write_iter+0x157/0x380 fs/read_write.c:517
 dump_emit_page+0x3de/0x830 fs/coredump.c:864
 dump_user_range+0x5e/0x200 fs/coredump.c:915
 elf_core_dump+0x1b4f/0x1c60 fs/binfmt_elf.c:2137
 do_coredump+0xed7/0x1790 fs/coredump.c:762
 get_signal+0xa04/0xc70 kernel/signal.c:2845
 arch_do_signal_or_restart+0x85/0x290 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop+0x78/0x130 kernel/entry/common.c:168
 exit_to_user_mode_prepare+0x69/0x90 kernel/entry/common.c:203
 irqentry_exit_to_user_mode+0x5/0x10 kernel/entry/common.c:309
 irqentry_exit+0xe/0x40 kernel/entry/common.c:412
 exc_general_protection+0x321/0x4b0 arch/x86/kernel/traps.c:728
 asm_exc_general_protection+0x22/0x30 arch/x86/include/asm/idtentry.h:564

read to 0xffffffff86eff0c0 of 4 bytes by task 22469 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:308

value changed: 0x0000020b -> 0x0000020c

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 22469 Comm: kworker/u4:0 Not tainted 6.1.0-syzkaller-14594-g72a85e2b0a1e-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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