syzbot

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BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

read-write to 0xffff88810164c920 of 8 bytes by task 22944 on cpu 0:
 percpu_counter_add_batch+0x110/0x130 lib/percpu_counter.c:107
 wb_stat_mod include/linux/backing-dev.h:66 [inline]
 folio_account_dirtied mm/page-writeback.c:2665 [inline]
 __folio_mark_dirty+0x2a7/0x4a0 mm/page-writeback.c:2717
 block_dirty_folio+0xd8/0x110 fs/buffer.c:754
 folio_mark_dirty+0x80/0xd0 mm/page-writeback.c:2825
 filemap_page_mkwrite+0x247/0x440 mm/filemap.c:3892
 do_page_mkwrite mm/memory.c:3488 [inline]
 wp_page_shared mm/memory.c:3889 [inline]
 do_wp_page+0xa77/0x2510 mm/memory.c:4108
 handle_pte_fault mm/memory.c:6193 [inline]
 __handle_mm_fault mm/memory.c:6318 [inline]
 handle_mm_fault+0x77d/0x2be0 mm/memory.c:6487
 do_user_addr_fault+0x3fe/0x1080 arch/x86/mm/fault.c:1387
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
 rep_movs_alternative+0x4a/0x90 arch/x86/lib/copy_user_64.S:68
 copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
 raw_copy_to_user arch/x86/include/asm/uaccess_64.h:147 [inline]
 copy_to_user_iter lib/iov_iter.c:25 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x141/0xe70 lib/iov_iter.c:185
 copy_to_iter include/linux/uio.h:220 [inline]
 get_random_bytes_user+0x12d/0x290 drivers/char/random.c:473
 __do_sys_getrandom drivers/char/random.c:1416 [inline]
 __se_sys_getrandom drivers/char/random.c:1390 [inline]
 __x64_sys_getrandom+0xcf/0x1a0 drivers/char/random.c:1390
 x64_sys_call+0x1fa6/0x3000 arch/x86/include/generated/asm/syscalls_64.h:319
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810164c920 of 8 bytes by task 323 on cpu 1:
 percpu_counter_read include/linux/percpu_counter.h:110 [inline]
 __wb_update_bandwidth+0x80/0x5d0 mm/page-writeback.c:1508
 wb_update_bandwidth+0x54/0x80 mm/page-writeback.c:1536
 wb_update_bandwidth_workfn+0x1c/0x30 mm/backing-dev.c:507
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3346
 worker_thread+0x582/0x770 kernel/workqueue.c:3427
 kthread+0x486/0x510 kernel/kthread.c:463
 ret_from_fork+0x11f/0x1b0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0000000000001b90 -> 0x0000000000001ba0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 323 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: writeback wb_update_bandwidth_workfn
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