syzbot

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BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

read-write to 0xffff888102361948 of 8 bytes by interrupt on cpu 0:
 percpu_counter_add_batch+0x110/0x130 lib/percpu_counter.c:107
 wb_stat_mod include/linux/backing-dev.h:66 [inline]
 __wb_writeout_add+0x42/0x1b0 mm/page-writeback.c:585
 __folio_end_writeback+0x200/0x470 mm/page-writeback.c:3030
 folio_end_writeback+0x71/0x3d0 mm/filemap.c:1660
 end_buffer_async_write+0x156/0x1f0 fs/buffer.c:419
 end_bio_bh_io_sync+0x79/0xa0 fs/buffer.c:2783
 bio_endio+0x377/0x410 block/bio.c:1645
 blk_update_request+0x336/0x730 block/blk-mq.c:987
 blk_mq_end_request+0x26/0x50 block/blk-mq.c:1149
 lo_complete_rq+0x98/0x140 drivers/block/loop.c:304
 blk_complete_reqs block/blk-mq.c:1224 [inline]
 blk_done_softirq+0x74/0xb0 block/blk-mq.c:1229
 handle_softirqs+0xba/0x290 kernel/softirq.c:579
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:968
 smpboot_thread_fn+0x32b/0x530 kernel/smpboot.c:164
 kthread+0x486/0x510 kernel/kthread.c:464
 ret_from_fork+0xdd/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888102361948 of 8 bytes by task 3310 on cpu 1:
 percpu_counter_read include/linux/percpu_counter.h:110 [inline]
 __wb_update_bandwidth+0x98/0x5d0 mm/page-writeback.c:1511
 wb_update_bandwidth mm/page-writeback.c:1538 [inline]
 do_writepages+0x2dd/0x310 mm/page-writeback.c:2659
 filemap_fdatawrite_wbc mm/filemap.c:386 [inline]
 __filemap_fdatawrite_range mm/filemap.c:419 [inline]
 __filemap_fdatawrite mm/filemap.c:425 [inline]
 filemap_flush+0xe4/0x120 mm/filemap.c:470
 sync_blockdev_nowait+0x29/0x40 block/bdev.c:248
 sync_filesystem+0xe2/0x190 fs/sync.c:60
 generic_shutdown_super+0x44/0x210 fs/super.c:622
 kill_block_super+0x2a/0x70 fs/super.c:1755
 ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7391
 deactivate_locked_super+0x72/0x1c0 fs/super.c:474
 deactivate_super+0x97/0xa0 fs/super.c:507
 cleanup_mnt+0x269/0x2e0 fs/namespace.c:1417
 __cleanup_mnt+0x19/0x20 fs/namespace.c:1424
 task_work_run+0x12e/0x1a0 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xe4/0x100 kernel/entry/common.c:114
 exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
 do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000450 -> 0x0000000000000460

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3310 Comm: syz-executor Tainted: G        W           6.16.0-rc2-syzkaller-00318-g739a6c93cc75 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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