[moderation] [fs?] [mm?] KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch (11)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2d1373e4246d Merge tag 'for-7.0-rc4-tag' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1750c216580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=44d083df850d93aad28d
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/b2aee7aa6da1/disk-2d1373e4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6cbfa1602880/vmlinux-2d1373e4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/52fe8db03e03/bzImage-2d1373e4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+44d083...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

read-write to 0xffff888101c20148 of 8 bytes by task 6120 on cpu 0:
percpu_counter_add_batch+0x105/0x130 lib/percpu_counter.c:107
wb_stat_mod include/linux/backing-dev.h:66 [inline]
__wb_writeout_add+0x42/0x1b0 mm/page-writeback.c:577
__folio_end_writeback+0x14b/0x360 mm/page-writeback.c:2953
folio_end_writeback_no_dropbehind+0x6d/0x1d0 mm/filemap.c:1666
folio_end_writeback+0x1c/0x70 mm/filemap.c:1692
mpage_write_end_io+0x270/0x630 fs/mpage.c:65
bio_endio+0x38a/0x420 block/bio.c:1792
submit_bio_noacct+0x76f/0x9b0 block/blk-core.c:891
submit_bio+0x2a4/0x2c0 block/blk-core.c:926
mpage_bio_submit_write fs/mpage.c:83 [inline]
mpage_write_folio fs/mpage.c:614 [inline]
mpage_writepages+0xaae/0x1310 fs/mpage.c:670
fat_writepages+0x24/0x30 fs/fat/inode.c:200
do_writepages+0x1c6/0x310 mm/page-writeback.c:2554
__writeback_single_inode+0x80/0x860 fs/fs-writeback.c:1750
writeback_sb_inodes+0x4fe/0xaf0 fs/fs-writeback.c:2042
wb_writeback+0x25f/0x5d0 fs/fs-writeback.c:2227
wb_do_writeback fs/fs-writeback.c:2374 [inline]
wb_workfn+0x1a5/0x970 fs/fs-writeback.c:2414
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3359
worker_thread+0x58a/0x780 kernel/workqueue.c:3440
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888101c20148 of 8 bytes by task 6001 on cpu 1:
percpu_counter_read include/linux/percpu_counter.h:110 [inline]
__wb_update_bandwidth+0x98/0x5d0 mm/page-writeback.c:1501
wb_update_bandwidth+0x54/0x80 mm/page-writeback.c:1528
wb_update_bandwidth_workfn+0x1c/0x30 mm/backing-dev.c:507
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3359
worker_thread+0x58a/0x780 kernel/workqueue.c:3440
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00000000000006b0 -> 0x00000000000006d0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 6001 Comm: kworker/u8:24 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: writeback wb_update_bandwidth_workfn
==================================================================


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