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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 58fdd8484c05 Merge tag 'sound-6.18-rc4' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148b9fe2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=63e0988e071251a5d8e9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/29a96f8ed3ff/disk-58fdd848.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5c6d128b5a4e/vmlinux-58fdd848.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d447b7f0f9c7/bzImage-58fdd848.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+63e098...@syzkaller.appspotmail.com

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

write to 0xffff888106e58c30 of 8 bytes by task 4039 on cpu 1:
__d_set_inode_and_type fs/dcache.c:406 [inline]
__d_instantiate+0x1f8/0x3b0 fs/dcache.c:1936
d_instantiate+0x59/0x80 fs/dcache.c:1963
shmem_mknod+0x153/0x180 mm/shmem.c:3864
shmem_create+0x34/0x50 mm/shmem.c:3917
lookup_open fs/namei.c:3796 [inline]
open_last_lookups fs/namei.c:3895 [inline]
path_openat+0x1105/0x2170 fs/namei.c:4131
do_filp_open+0x109/0x230 fs/namei.c:4161
do_sys_openat2+0xa6/0x110 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_creat fs/open.c:1530 [inline]
__se_sys_creat fs/open.c:1524 [inline]
__x64_sys_creat+0x65/0x90 fs/open.c:1524
x64_sys_call+0x2da3/0x3000 arch/x86/include/generated/asm/syscalls_64.h:86
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

read to 0xffff888106e58c30 of 8 bytes by task 4040 on cpu 0:
lookup_fast_for_open fs/namei.c:3839 [inline]
open_last_lookups fs/namei.c:3866 [inline]
path_openat+0x45e/0x2170 fs/namei.c:4131
do_filp_open+0x109/0x230 fs/namei.c:4161
do_sys_openat2+0xa6/0x110 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_creat fs/open.c:1530 [inline]
__se_sys_creat fs/open.c:1524 [inline]
__x64_sys_creat+0x65/0x90 fs/open.c:1524
x64_sys_call+0x2da3/0x3000 arch/x86/include/generated/asm/syscalls_64.h:86
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: 0x0000000000000000 -> 0xffff888129d67aa0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4040 Comm: syz.4.23246 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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