[moderation] [fs?] KCSAN: data-race in __d_instantiate / step_into (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cd5a0afbdf80 Merge tag 'mailbox-v6.18' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=128e1892580000
kernel config: https://syzkaller.appspot.com/x/.config?x=655a48029989f36f
dashboard link: https://syzkaller.appspot.com/bug?extid=caa50c66a4208e1090fb
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/1d38d44fa88c/disk-cd5a0afb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6f64cc50d445/vmlinux-cd5a0afb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/46764ef5440b/bzImage-cd5a0afb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+caa50c...@syzkaller.appspotmail.com

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

write to 0xffff888106debdb0 of 8 bytes by task 4022 on cpu 0:
__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_symlink+0x3a7/0x3d0 mm/shmem.c:4136
vfs_symlink+0xd4/0x1e0 fs/namei.c:4817
do_symlinkat+0xc7/0x3c0 fs/namei.c:4843
__do_sys_symlink fs/namei.c:4864 [inline]
__se_sys_symlink fs/namei.c:4862 [inline]
__x64_sys_symlink+0x50/0x60 fs/namei.c:4862
x64_sys_call+0x23d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:89
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 0xffff888106debdb0 of 8 bytes by task 3001 on cpu 1:
step_into+0x122/0x7f0 fs/namei.c:1993
walk_component+0x162/0x220 fs/namei.c:2157
lookup_last fs/namei.c:2652 [inline]
path_lookupat+0xfe/0x2a0 fs/namei.c:2676
filename_lookup+0x147/0x340 fs/namei.c:2705
do_readlinkat+0x7d/0x320 fs/stat.c:576
__do_sys_readlink fs/stat.c:613 [inline]
__se_sys_readlink fs/stat.c:610 [inline]
__x64_sys_readlink+0x47/0x60 fs/stat.c:610
x64_sys_call+0x28de/0x3000 arch/x86/include/generated/asm/syscalls_64.h:90
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 -> 0xffff88811b8c37b8

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3001 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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