[moderation] [fs?] KCSAN: data-race in __d_instantiate / step_into (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2f91ff27b0ee Merge tag 'sound-6.12-rc2' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17b2d380580000
kernel config: https://syzkaller.appspot.com/x/.config?x=95098faba89c70c9
dashboard link: https://syzkaller.appspot.com/bug?extid=7e4c7c12527faec11941
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/14933c4ac457/disk-2f91ff27.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6725831fc1a1/vmlinux-2f91ff27.xz
kernel image: https://storage.googleapis.com/syzbot-assets/98d64e038e72/bzImage-2f91ff27.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7e4c7c...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_instantiate / step_into

read-write to 0xffff88810649c9c0 of 4 bytes by task 3258 on cpu 0:
__d_instantiate+0x2d5/0x3c0 fs/dcache.c:1869
d_instantiate+0x59/0x80 fs/dcache.c:1894
shmem_symlink+0x36a/0x3a0 mm/shmem.c:3847
vfs_symlink+0xca/0x1d0 fs/namei.c:4615
do_symlinkat+0xe3/0x350 fs/namei.c:4641
__do_sys_symlink fs/namei.c:4662 [inline]
__se_sys_symlink fs/namei.c:4660 [inline]
__x64_sys_symlink+0x50/0x60 fs/namei.c:4660
x64_sys_call+0x2819/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:89
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810649c9c0 of 4 bytes by task 2967 on cpu 1:
__follow_mount_rcu fs/namei.c:1511 [inline]
handle_mounts fs/namei.c:1562 [inline]
step_into+0xe7/0x810 fs/namei.c:1891
walk_component+0x169/0x230 fs/namei.c:2059
lookup_last fs/namei.c:2556 [inline]
path_lookupat+0x10a/0x2b0 fs/namei.c:2580
filename_lookup+0x127/0x300 fs/namei.c:2609
do_readlinkat+0x89/0x210 fs/stat.c:537
__do_sys_readlink fs/stat.c:574 [inline]
__se_sys_readlink fs/stat.c:571 [inline]
__x64_sys_readlink+0x47/0x60 fs/stat.c:571
x64_sys_call+0x13c3/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:90
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000008 -> 0x00600008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2967 Comm: udevd Tainted: G W 6.12.0-rc1-syzkaller-00257-g2f91ff27b0ee #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup