[moderation] [fs?] KCSAN: data-race in __d_instantiate / lookup_fast (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8cf0b93919e1 Linux 6.12-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=112927d0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a2f7ae2f221e9eae
dashboard link: https://syzkaller.appspot.com/bug?extid=5851a71d4b8edd2f0f95
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/8f5ff8e3b043/disk-8cf0b939.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8d714b153cdb/vmlinux-8cf0b939.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dd32c91c7643/bzImage-8cf0b939.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5851a7...@syzkaller.appspotmail.com

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

read-write to 0xffff8881065a3b40 of 4 bytes by task 3255 on cpu 1:
__d_instantiate+0x2d5/0x3c0 fs/dcache.c:1869
d_instantiate+0x59/0x80 fs/dcache.c:1894
shmem_symlink+0x36a/0x3a0 mm/shmem.c:3847
vfs_symlink+0xca/0x1d0 fs/namei.c:4615
do_symlinkat+0xe3/0x350 fs/namei.c:4641
__do_sys_symlink fs/namei.c:4662 [inline]
__se_sys_symlink fs/namei.c:4660 [inline]
__x64_sys_symlink+0x50/0x60 fs/namei.c:4660
x64_sys_call+0x2819/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:89
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881065a3b40 of 4 bytes by task 2966 on cpu 0:
d_revalidate fs/namei.c:867 [inline]
lookup_fast+0xd9/0x2a0 fs/namei.c:1681
walk_component+0x3f/0x230 fs/namei.c:2049
lookup_last fs/namei.c:2556 [inline]
path_lookupat+0x10a/0x2b0 fs/namei.c:2580
filename_lookup+0x127/0x300 fs/namei.c:2609
do_readlinkat+0x89/0x210 fs/stat.c:537
__do_sys_readlink fs/stat.c:574 [inline]
__se_sys_readlink fs/stat.c:571 [inline]
__x64_sys_readlink+0x47/0x60 fs/stat.c:571
x64_sys_call+0x13c3/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:90
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000008 -> 0x00600008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2966 Comm: udevd Not tainted 6.12.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================


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[syzbot]

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