[moderation] [exfat?] KCSAN: data-race in __generic_file_fsync / writeback_sb_inodes

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 30d4efb2f5a5 Merge tag 'for-linus-6.18-rc1-tag' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=111a96e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9747ee9dea2e604b
dashboard link: https://syzkaller.appspot.com/bug?extid=6dd548ddb6c342e516f3
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [hiro...@mail.parknet.co.jp linki...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org sj155...@samsung.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fc8538e56ea4/disk-30d4efb2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d670412a4674/vmlinux-30d4efb2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5730e382c3d2/bzImage-30d4efb2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6dd548...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __generic_file_fsync / writeback_sb_inodes

write to 0xffff888119c8b728 of 4 bytes by task 51 on cpu 1:
writeback_sb_inodes+0x33d/0xa30 fs/fs-writeback.c:2004
__writeback_inodes_wb+0x94/0x1a0 fs/fs-writeback.c:2086
wb_writeback+0x266/0x5c0 fs/fs-writeback.c:2197
wb_check_start_all fs/fs-writeback.c:2323 [inline]
wb_do_writeback fs/fs-writeback.c:2349 [inline]
wb_workfn+0x4c9/0x910 fs/fs-writeback.c:2382
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3319
worker_thread+0x582/0x770 kernel/workqueue.c:3400
kthread+0x486/0x510 kernel/kthread.c:463
ret_from_fork+0x11f/0x1b0 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888119c8b728 of 4 bytes by task 5187 on cpu 0:
__generic_file_fsync+0x94/0x140 fs/libfs.c:1545
fat_file_fsync+0x49/0x100 fs/fat/file.c:191
vfs_fsync_range+0x10d/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3036 [inline]
generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4322
iter_file_splice_write+0x663/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x153/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x30f/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+0x2bb0/0x2ff0 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: 0x00020070 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5187 Comm: syz.2.636 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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