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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 502d801f0ab0 Merge tag 'erofs-for-7.2-rc1' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1111701c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d0f6c16a80c07db
dashboard link: https://syzkaller.appspot.com/bug?extid=c900d69656aab3702986
compiler: Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
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/7a2ab34be1f7/disk-502d801f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/344e858ce175/vmlinux-502d801f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/269d734808e7/bzImage-502d801f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c900d6...@syzkaller.appspotmail.com

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

read-write to 0xffff888100414780 of 4 bytes by task 3289 on cpu 0:
fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
__d_instantiate+0x2a8/0x390 fs/dcache.c:2149
d_make_persistent+0x72/0x110 fs/dcache.c:2973
shmem_symlink+0x386/0x3a0 mm/shmem.c:4068
vfs_symlink+0xfd/0x220 fs/namei.c:5656
filename_symlinkat+0xe8/0x2b0 fs/namei.c:5681
__do_sys_symlink fs/namei.c:5708 [inline]
__se_sys_symlink+0x42/0x1b0 fs/namei.c:5704
__x64_sys_symlink+0x31/0x40 fs/namei.c:5704
x64_sys_call+0x2465/0x3020 arch/x86/include/generated/asm/syscalls_64.h:89
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888100414780 of 4 bytes by task 2979 on cpu 1:
d_managed include/linux/dcache.h:433 [inline]
step_into fs/namei.c:2140 [inline]
walk_component fs/namei.c:2288 [inline]
lookup_last fs/namei.c:2789 [inline]
path_lookupat+0x19b/0x4c0 fs/namei.c:2813
filename_lookup+0x18f/0x390 fs/namei.c:2842
do_readlinkat+0x74/0x2f0 fs/stat.c:571
__do_sys_readlink fs/stat.c:605 [inline]
__se_sys_readlink fs/stat.c:602 [inline]
__x64_sys_readlink+0x47/0x60 fs/stat.c:602
x64_sys_call+0x2b51/0x3020 arch/x86/include/generated/asm/syscalls_64.h:90
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000080 -> 0x08300080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2979 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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