[moderation] [fs?] KCSAN: data-race in dentry_unlink_inode / step_into_slowpath

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1d18101a644e Merge tag 'kernel-6.19-rc1.cred' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1544e512580000
kernel config: https://syzkaller.appspot.com/x/.config?x=655255e3ef31c19b
dashboard link: https://syzkaller.appspot.com/bug?extid=6b0be41ebcb0c7cd64a5
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/db533fa62653/disk-1d18101a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ab12e3cf501d/vmlinux-1d18101a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f3e77af82775/bzImage-1d18101a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6b0be4...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in dentry_unlink_inode / step_into_slowpath

write to 0xffff88810044f570 of 8 bytes by task 3305 on cpu 1:
__d_clear_type_and_inode fs/dcache.c:420 [inline]
dentry_unlink_inode+0x65/0x260 fs/dcache.c:457
d_delete+0x164/0x180 fs/dcache.c:2479
d_delete_notify+0x32/0x100 include/linux/fsnotify.h:375
vfs_unlink+0x30b/0x420 fs/namei.c:4758
do_unlinkat+0x24e/0x480 fs/namei.c:4807
__do_sys_unlink fs/namei.c:4853 [inline]
__se_sys_unlink fs/namei.c:4851 [inline]
__x64_sys_unlink+0x2e/0x40 fs/namei.c:4851
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+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810044f570 of 8 bytes by task 3004 on cpu 0:
step_into_slowpath+0x113/0x480 fs/namei.c:2046
step_into fs/namei.c:2091 [inline]
walk_component fs/namei.c:2227 [inline]
lookup_last fs/namei.c:2722 [inline]
path_lookupat+0x330/0x500 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+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811a2f0c20 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3004 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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