[moderation] [block?] KCSAN: data-race in _copy_to_iter / kmmpd (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4427259cc7f7 Merge tag 'riscv-for-linus-6.18-rc6' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12710692580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=e758b85478117a603508
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ax...@kernel.dk linux...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e7ffe3a81af7/disk-4427259c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ad2636df3670/vmlinux-4427259c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0aadfe5da806/bzImage-4427259c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e758b8...@syzkaller.appspotmail.com

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

read to 0xffff888107887000 of 512 bytes by task 3306 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:302 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
_copy_to_iter+0x130/0xe70 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:2799
blkdev_read_iter+0x22d/0x2e0 block/fops.c:859
new_sync_read fs/read_write.c:491 [inline]
vfs_read+0x64c/0x770 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+0x27c0/0x3000 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

write to 0xffff888107887010 of 64 bytes by task 3710 on cpu 0:
kmmpd+0x104/0x670 fs/ext4/mmp.c:162
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3710 Comm: kmmpd-loop2 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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