[moderation] [exfat?] KCSAN: data-race in _copy_to_iter / fat_clusters_flush

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: babe393974de Merge tag 'docs-6.7' of git://git.lwn.net/linux
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116fe3e7680000
kernel config: https://syzkaller.appspot.com/x/.config?x=561f2d77dae76e1b
dashboard link: https://syzkaller.appspot.com/bug?extid=3830a056dc3f6d5c206d
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/77df7f740b2a/disk-babe3939.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b625c5f3c241/vmlinux-babe3939.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d75a0fa6f022/bzImage-babe3939.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3830a0...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat_clusters_flush

write to 0xffff8881507193e8 of 4 bytes by task 2437 on cpu 0:
fat_clusters_flush+0x137/0x210 fs/fat/misc.c:93
fat_write_inode+0x72/0xd0 fs/fat/inode.c:919
write_inode fs/fs-writeback.c:1473 [inline]
__writeback_single_inode+0x34f/0x860 fs/fs-writeback.c:1690
writeback_sb_inodes+0x514/0xad0 fs/fs-writeback.c:1916
wb_writeback+0x252/0x6e0 fs/fs-writeback.c:2092
wb_do_writeback fs/fs-writeback.c:2239 [inline]
wb_workfn+0x1a8/0x8d0 fs/fs-writeback.c:2279
process_one_work kernel/workqueue.c:2630 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703
worker_thread+0x525/0x730 kernel/workqueue.c:2784
kthread+0x1d7/0x210 kernel/kthread.c:388
ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

read to 0xffff888150719000 of 1024 bytes by task 3432 on cpu 1:
instrument_copy_to_user include/linux/instrumented.h:113 [inline]
copy_to_user_iter lib/iov_iter.c:24 [inline]
iterate_ubuf include/linux/iov_iter.h:29 [inline]
iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
iterate_and_advance include/linux/iov_iter.h:271 [inline]
_copy_to_iter+0x126/0xb20 lib/iov_iter.c:186
copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:381
copy_folio_to_iter include/linux/uio.h:181 [inline]
filemap_read+0x424/0x680 mm/filemap.c:2703
blkdev_read_iter+0x217/0x2c0 block/fops.c:742
call_read_iter include/linux/fs.h:2014 [inline]
new_sync_read fs/read_write.c:389 [inline]
vfs_read+0x3c0/0x590 fs/read_write.c:470
ksys_read+0xeb/0x1a0 fs/read_write.c:613
__do_sys_read fs/read_write.c:623 [inline]
__se_sys_read fs/read_write.c:621 [inline]
__x64_sys_read+0x42/0x50 fs/read_write.c:621
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3432 Comm: udevd Not tainted 6.6.0-syzkaller-10265-gbabe393974de #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
==================================================================
I/O error, dev loop2, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop2, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.