[moderation] [fs?] KCSAN: data-race in __d_lookup_rcu / __d_rehash (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 87adedeba51a Merge tag 'net-6.8-rc7' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12aa20ca180000
kernel config: https://syzkaller.appspot.com/x/.config?x=53006d590acdf777
dashboard link: https://syzkaller.appspot.com/bug?extid=e2f256d639284c733c14
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/85879d80665b/disk-87adedeb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/594eb01e8ed8/vmlinux-87adedeb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c4cbd4a49e35/bzImage-87adedeb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e2f256...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_lookup_rcu / __d_rehash

read to 0xffff8881636eb850 of 8 bytes by task 6795 on cpu 0:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:342 [inline]
__d_lookup_rcu+0x120/0x290 fs/dcache.c:2224
lookup_fast+0x8e/0x290 fs/namei.c:1628
walk_component+0x3f/0x230 fs/namei.c:2001
lookup_last fs/namei.c:2462 [inline]
path_lookupat+0x10a/0x2a0 fs/namei.c:2486
filename_lookup+0x126/0x300 fs/namei.c:2515
vfs_statx+0xa2/0x320 fs/stat.c:244
vfs_fstatat+0xcd/0x100 fs/stat.c:304
__do_sys_newfstatat fs/stat.c:468 [inline]
__se_sys_newfstatat+0x58/0x260 fs/stat.c:462
__x64_sys_newfstatat+0x55/0x60 fs/stat.c:462
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

write to 0xffff8881636eb850 of 8 bytes by task 2774 on cpu 1:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0xc4/0x220 fs/dcache.c:2403
__d_add+0x36d/0x4a0 fs/dcache.c:2618
d_add+0x45/0x50 fs/dcache.c:2641
simple_lookup+0x89/0xa0 fs/libfs.c:79
lookup_one_qstr_excl+0xc0/0x180 fs/namei.c:1608
do_unlinkat+0x144/0x4c0 fs/namei.c:4390
__do_sys_unlink fs/namei.c:4450 [inline]
__se_sys_unlink fs/namei.c:4448 [inline]
__x64_sys_unlink+0x30/0x40 fs/namei.c:4448
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2774 Comm: udevd Not tainted 6.8.0-rc6-syzkaller-00120-g87adedeba51a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
==================================================================


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[syzbot]

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