[moderation] [ext4?] KCSAN: data-race in generic_buffers_fsync_noflush / move_expired_inodes

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1f4a222b0e33 Remove long-stale ext3 defconfig option
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1093ac58580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bafeb347352dd60e
dashboard link: https://syzkaller.appspot.com/bug?extid=125ac6db3d22bc21c495
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/785e68511950/disk-1f4a222b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2366f9786f09/vmlinux-1f4a222b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1ec7c0f5bb09/bzImage-1f4a222b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+125ac6...@syzkaller.appspotmail.com

loop5: detected capacity change from 0 to 1024
==================================================================
BUG: KCSAN: data-race in generic_buffers_fsync_noflush / move_expired_inodes

read-write to 0xffff888145db2d10 of 4 bytes by task 3695 on cpu 1:
move_expired_inodes+0x17a/0x400 fs/fs-writeback.c:1496
queue_io+0xd9/0x2c0 fs/fs-writeback.c:1548
wb_writeback+0x226/0x5c0 fs/fs-writeback.c:2191
wb_do_writeback fs/fs-writeback.c:2342 [inline]
wb_workfn+0x194/0x910 fs/fs-writeback.c:2382
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3346
worker_thread+0x582/0x770 kernel/workqueue.c:3427
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888145db2d10 of 4 bytes by task 1001 on cpu 0:
generic_buffers_fsync_noflush+0x80/0x120 fs/buffer.c:614
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:187
generic_write_sync include/linux/fs.h:3046 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_file_write_iter+0x387/0xf60 fs/ext4/file.c:-1
iter_file_splice_write+0x666/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2bb4/0x3000 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000070 -> 0x00020002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 1001 Comm: syz.5.8922 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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