[moderation] [mm?] [fs?] KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 739a6c93cc75 Merge tag 'nfsd-6.16-1' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11150b0c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=25d7df3a6a1d1ea6
dashboard link: https://syzkaller.appspot.com/bug?extid=ade9a83b6ae7a3c3c3fe
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@kvack.org wi...@infradead.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/218c10526673/disk-739a6c93.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0c623ab29780/vmlinux-739a6c93.xz
kernel image: https://storage.googleapis.com/syzbot-assets/02fd1236371b/bzImage-739a6c93.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ade9a8...@syzkaller.appspotmail.com

==================================================================
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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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.