[moderation] [fs?] KCSAN: data-race in __d_instantiate / lookup_fast (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3d413f0cfd7e Merge tag 'audit-pr-20250527' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b1fbf4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3af56729e26be7d
dashboard link: https://syzkaller.appspot.com/bug?extid=05fea4c74ecfd1819278
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/97acdca9a9a2/disk-3d413f0c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7c50fd817f1c/vmlinux-3d413f0c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a4e67928f8ac/bzImage-3d413f0c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+05fea4...@syzkaller.appspotmail.com

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

read-write to 0xffff888100718f00 of 4 bytes by task 3527 on cpu 0:
fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
__d_instantiate+0x2c2/0x3b0 fs/dcache.c:1922
d_instantiate+0x59/0x80 fs/dcache.c:1947
shmem_symlink+0x3a7/0x3d0 mm/shmem.c:4132
vfs_symlink+0xd4/0x1e0 fs/namei.c:4730
do_symlinkat+0xc7/0x3c0 fs/namei.c:4756
__do_sys_symlink fs/namei.c:4777 [inline]
__se_sys_symlink fs/namei.c:4775 [inline]
__x64_sys_symlink+0x50/0x60 fs/namei.c:4775
x64_sys_call+0x2d8d/0x2fb0 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 0xffff888100718f00 of 4 bytes by task 3009 on cpu 1:
d_revalidate fs/namei.c:928 [inline]
lookup_fast+0xf0/0x320 fs/namei.c:1765
walk_component+0x3f/0x220 fs/namei.c:2134
lookup_last fs/namei.c:2639 [inline]
path_lookupat+0xfe/0x2a0 fs/namei.c:2663
filename_lookup+0x147/0x340 fs/namei.c:2692
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+0x2cf3/0x2fb0 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: 0x00000008 -> 0x00300008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3009 Comm: udevd Not tainted 6.15.0-syzkaller-03645-g3d413f0cfd7e #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.