[moderation] [fs?] KCSAN: data-race in d_make_discardable / path_lookupat

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc3ee4ba57b7 Merge tag 'x86-urgent-2025-12-06' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=140e26c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=70709f84a6900d56
dashboard link: https://syzkaller.appspot.com/bug?extid=59084ea90b24f42b504e
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/7e4e4631f374/disk-cc3ee4ba.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9b3bc364e37c/vmlinux-cc3ee4ba.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6f4bd14ab533/bzImage-cc3ee4ba.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+59084e...@syzkaller.appspotmail.com

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

write to 0xffff888110d9dc00 of 4 bytes by task 14976 on cpu 1:
d_make_discardable+0x4f/0xa0 fs/dcache.c:936
simple_unlink+0x68/0x80 fs/libfs.c:815
shmem_unlink+0x12d/0x140 mm/shmem.c:3980
vfs_unlink+0x28b/0x440 fs/namei.c:5369
do_unlinkat+0x1cd/0x4b0 fs/namei.c:5439
__do_sys_unlink fs/namei.c:5474 [inline]
__se_sys_unlink fs/namei.c:5472 [inline]
__x64_sys_unlink+0x2e/0x40 fs/namei.c:5472
x64_sys_call+0x2f48/0x3000 arch/x86/include/generated/asm/syscalls_64.h:88
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888110d9dc00 of 4 bytes by task 3011 on cpu 0:
d_managed include/linux/dcache.h:403 [inline]
step_into fs/namei.c:2078 [inline]
walk_component fs/namei.c:2227 [inline]
lookup_last fs/namei.c:2722 [inline]
path_lookupat+0x1d8/0x500 fs/namei.c:2746
filename_lookup+0x147/0x340 fs/namei.c:2775
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+0x2af1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:90
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x08300080 -> 0x00004080

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3011 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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