[moderation] [fs?] KCSAN: data-race in __dentry_kill / step_into (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 96fca68c4fbf Merge tag 'nfsd-6.9-3' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=161cb7db180000
kernel config: https://syzkaller.appspot.com/x/.config?x=eaea34ec4c9b6fb6
dashboard link: https://syzkaller.appspot.com/bug?extid=75d9430d2a5664490007
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/c847bdb99fa5/disk-96fca68c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7f1451b82626/vmlinux-96fca68c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dc96a83503e5/bzImage-96fca68c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+75d943...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __dentry_kill / step_into

read-write to 0xffff888100541300 of 4 bytes by task 22580 on cpu 1:
dentry_unlist fs/dcache.c:548 [inline]
__dentry_kill+0x228/0x4b0 fs/dcache.c:617
shrink_kill fs/dcache.c:1048 [inline]
shrink_dentry_list+0x1bc/0x3e0 fs/dcache.c:1075
shrink_dcache_sb+0x165/0x2a0 fs/dcache.c:1195
reconfigure_super+0x3fe/0x5a0 fs/super.c:1049
do_remount fs/namespace.c:2892 [inline]
path_mount+0x96e/0xb30 fs/namespace.c:3671
do_mount fs/namespace.c:3692 [inline]
__do_sys_mount fs/namespace.c:3898 [inline]
__se_sys_mount+0x27f/0x2d0 fs/namespace.c:3875
__x64_sys_mount+0x67/0x80 fs/namespace.c:3875
x64_sys_call+0x2591/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:166
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+0x77/0x7f

read to 0xffff888100541300 of 4 bytes by task 18907 on cpu 0:
__d_entry_type include/linux/dcache.h:397 [inline]
d_is_symlink include/linux/dcache.h:427 [inline]
step_into+0x12f/0x810 fs/namei.c:1847
open_last_lookups fs/namei.c:3589 [inline]
path_openat+0x10fc/0x1d80 fs/namei.c:3796
do_filp_open+0xf7/0x200 fs/namei.c:3826
do_sys_openat2+0xab/0x120 fs/open.c:1406
do_sys_open fs/open.c:1421 [inline]
__do_sys_openat fs/open.c:1437 [inline]
__se_sys_openat fs/open.c:1432 [inline]
__x64_sys_openat+0xf3/0x120 fs/open.c:1432
x64_sys_call+0x2cad/0x2d30 arch/x86/include/generated/asm/syscalls_64.h:258
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+0x77/0x7f

value changed: 0x00200000 -> 0x00008000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18907 Comm: syz-executor.3 Not tainted 6.9.0-rc4-syzkaller-00031-g96fca68c4fbf #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
==================================================================
EXT4-fs (loop3): unmounting filesystem 00000000-0000-0000-0000-000000000000.
EXT4-fs (loop3): unmounting filesystem 00000000-0000-0000-0000-000000000000.


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