[moderation] [fs?] KCSAN: data-race in dont_mount / lookup_fast

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9ace34a8e446 Merge tag 'cgroup-for-6.7-rc4-fixes' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12c6f536e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=ac34c1f29a8029df
dashboard link: https://syzkaller.appspot.com/bug?extid=66941b35e83b90763e23
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [bra...@kernel.org 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/955528ed37c5/disk-9ace34a8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ed03c0892611/vmlinux-9ace34a8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b4d56563956a/bzImage-9ace34a8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+66941b...@syzkaller.appspotmail.com

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

read-write to 0xffff8881066f9180 of 4 bytes by task 3871 on cpu 0:
dont_mount+0x27/0x40 include/linux/dcache.h:352
vfs_unlink+0x282/0x3e0 fs/namei.c:4320
do_unlinkat+0x236/0x4c0 fs/namei.c:4382
__do_sys_unlink fs/namei.c:4430 [inline]
__se_sys_unlink fs/namei.c:4428 [inline]
__x64_sys_unlink+0x30/0x40 fs/namei.c:4428
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff8881066f9180 of 4 bytes by task 2778 on cpu 1:
d_revalidate fs/namei.c:861 [inline]
lookup_fast+0xd9/0x290 fs/namei.c:1643
walk_component+0x3f/0x230 fs/namei.c:1998
lookup_last fs/namei.c:2459 [inline]
path_lookupat+0x10a/0x2a0 fs/namei.c:2483
filename_lookup+0x126/0x300 fs/namei.c:2512
user_path_at_empty+0x42/0x110 fs/namei.c:2911
do_readlinkat+0x92/0x210 fs/stat.c:494
__do_sys_readlink fs/stat.c:527 [inline]
__se_sys_readlink fs/stat.c:524 [inline]
__x64_sys_readlink+0x47/0x50 fs/stat.c:524
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x00600008 -> 0x00008008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2778 Comm: udevd Not tainted 6.7.0-rc4-syzkaller-00039-g9ace34a8e446 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
==================================================================


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