[moderation] [ext4?] KCSAN: data-race in _copy_to_iter / kmmpd (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 733923397fd9 Merge tag 'pwm/for-6.16-rc6-fixes' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17449a8c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a2f5ccd29a82f8aa
dashboard link: https://syzkaller.appspot.com/bug?extid=10864d7b36df9a8f8750
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
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/eb595ef9a738/disk-73392339.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/da7013ae6197/vmlinux-73392339.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fd6bb59c6030/bzImage-73392339.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+10864d...@syzkaller.appspotmail.com

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

write to 0xffff88811d340008 of 8 bytes by task 5234 on cpu 0:
kmmpd+0xb7/0x660 fs/ext4/mmp.c:153
kthread+0x489/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff88811d340000 of 512 bytes by task 4584 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:30 [inline]
iterate_and_advance2 include/linux/iov_iter.h:300 [inline]
iterate_and_advance include/linux/iov_iter.h:328 [inline]
_copy_to_iter+0x12d/0xe30 lib/iov_iter.c:185
copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x407/0xa00 mm/filemap.c:2762
blkdev_read_iter+0x22d/0x2e0 block/fops.c:833
new_sync_read fs/read_write.c:491 [inline]
vfs_read+0x5ca/0x6f0 fs/read_write.c:572
ksys_read+0xda/0x1a0 fs/read_write.c:715
__do_sys_read fs/read_write.c:724 [inline]
__se_sys_read fs/read_write.c:722 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:722
x64_sys_call+0x2d77/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:1
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4584 Comm: udevd Not tainted 6.16.0-rc5-syzkaller-00038-g733923397fd9 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

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