[moderation] [fs?] KCSAN: data-race in __dentry_kill / d_alloc_parallel (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 17bbde2e1716 Merge tag 'net-6.16-rc5' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1723ac8c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=eea96b85b0259840
dashboard link: https://syzkaller.appspot.com/bug?extid=2aec59abff0dc8c53a9b
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
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/61f5389fb1d4/disk-17bbde2e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/37120745fd46/vmlinux-17bbde2e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/420fdeb92784/bzImage-17bbde2e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2aec59...@syzkaller.appspotmail.com

loop3: detected capacity change from 0 to 1024
EXT4-fs: Ignoring removed bh option
EXT4-fs (loop3): can't mount with data=, fs mounted w/o journal
==================================================================
BUG: KCSAN: data-race in __dentry_kill / d_alloc_parallel

read-write to 0xffff888106da1480 of 4 bytes by task 9092 on cpu 1:
d_alloc_parallel+0xa8e/0xc40 fs/dcache.c:2624
__lookup_slow+0x8c/0x250 fs/namei.c:1802
lookup_slow+0x3c/0x60 fs/namei.c:1834
walk_component+0x1ec/0x220 fs/namei.c:2138
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

read to 0xffff888106da1480 of 4 bytes by task 9075 on cpu 0:
dentry_unlist fs/dcache.c:639 [inline]
__dentry_kill+0x2aa/0x4b0 fs/dcache.c:683
dput+0x5e/0xd0 fs/dcache.c:911
handle_mounts fs/namei.c:1640 [inline]
step_into+0x5b2/0x820 fs/namei.c:1976
walk_component+0x162/0x220 fs/namei.c:2144
lookup_last fs/namei.c:2639 [inline]
path_lookupat+0xfe/0x2a0 fs/namei.c:2663
filename_lookup+0x147/0x340 fs/namei.c:2692
user_path_at+0x3e/0x130 fs/namei.c:3136
__do_sys_chdir fs/open.c:560 [inline]
__se_sys_chdir+0x45/0x1b0 fs/open.c:554
__x64_sys_chdir+0x1f/0x30 fs/open.c:554
x64_sys_call+0x2ad8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:81
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: 0x00000000 -> 0x01000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 9075 Comm: syz.3.1571 Tainted: G W 6.16.0-rc4-syzkaller-00108-g17bbde2e1716 #0 PREEMPT(voluntary)
Tainted: [W]=WARN
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.