syzbot

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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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