syzbot

EXT4-fs (loop4): can't get journal size
EXT4-fs (loop4): 1 truncate cleaned up
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BUG: KCSAN: data-race in __wb_update_bandwidth / percpu_counter_add_batch

read-write to 0xffff88810198b948 of 8 bytes by interrupt on cpu 1:
 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+0x14b/0x360 mm/page-writeback.c:2997
 folio_end_writeback_no_dropbehind+0x6d/0x1b0 mm/filemap.c:1661
 folio_end_writeback+0x1c/0x70 mm/filemap.c:1687
 ext4_finish_bio+0x459/0x8c0 fs/ext4/page-io.c:144
 ext4_end_bio+0x27b/0x380 fs/ext4/page-io.c:392
 bio_endio+0x37e/0x420 block/bio.c:1675
 blk_update_request+0x336/0x730 block/blk-mq.c:1007
 blk_mq_end_request+0x26/0x50 block/blk-mq.c:1169
 lo_complete_rq+0x98/0x140 drivers/block/loop.c:314
 blk_complete_reqs block/blk-mq.c:1244 [inline]
 blk_done_softirq+0x77/0xb0 block/blk-mq.c:1249
 handle_softirqs+0xba/0x290 kernel/softirq.c:622
 run_ksoftirqd+0x1c/0x30 kernel/softirq.c:1063
 smpboot_thread_fn+0x32b/0x530 kernel/smpboot.c:160
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff88810198b948 of 8 bytes by task 5004 on cpu 0:
 percpu_counter_read include/linux/percpu_counter.h:110 [inline]
 __wb_update_bandwidth+0x98/0x5d0 mm/page-writeback.c:1509
 wb_update_bandwidth mm/page-writeback.c:1536 [inline]
 do_writepages+0x2dd/0x310 mm/page-writeback.c:2621
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 file_write_and_wait_range+0x156/0x2c0 mm/filemap.c:786
 generic_buffers_fsync_noflush+0x45/0x130 fs/buffer.c:609
 ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
 ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
 vfs_fsync_range+0x10d/0x130 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2616 [inline]
 ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
 ext4_file_write_iter+0x387/0xf60 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x52a/0x960 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000150 -> 0x0000000000000160

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5004 Comm: syz.4.476 Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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