[moderation] [fs?] KCSAN: data-race in __lookup_mnt / attach_recursive_mnt

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4099a71718b0 Merge tag 'sched-urgent-2024-12-29' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=151d70b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=87d3cfca6847d1fa
dashboard link: https://syzkaller.appspot.com/bug?extid=ed521050420ad9c8b0ac
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/d71110f07633/disk-4099a717.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3d1a633db8fd/vmlinux-4099a717.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a1595c8cb5a0/bzImage-4099a717.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ed5210...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __lookup_mnt / attach_recursive_mnt

write to 0xffff888118555398 of 8 bytes by task 29882 on cpu 1:
unhash_mnt fs/namespace.c:998 [inline]
attach_recursive_mnt+0x81a/0xff0 fs/namespace.c:2500
do_move_mount+0x478/0x550 fs/namespace.c:3346
do_move_mount_old+0xa0/0xd0 fs/namespace.c:3378
path_mount+0x536/0xb30 fs/namespace.c:3832
do_mount fs/namespace.c:3847 [inline]
__do_sys_mount fs/namespace.c:4057 [inline]
__se_sys_mount+0x27c/0x2d0 fs/namespace.c:4034
__x64_sys_mount+0x67/0x80 fs/namespace.c:4034
x64_sys_call+0x2c84/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888118555398 of 8 bytes by task 29883 on cpu 0:
__lookup_mnt+0xa0/0xf0 fs/namespace.c:807
__follow_mount_rcu fs/namei.c:1591 [inline]
handle_mounts fs/namei.c:1621 [inline]
step_into+0x434/0x840 fs/namei.c:1950
walk_component+0x169/0x230 fs/namei.c:2118
lookup_last fs/namei.c:2610 [inline]
path_lookupat+0x10a/0x2b0 fs/namei.c:2634
filename_lookup+0x150/0x340 fs/namei.c:2663
kern_path+0x39/0x120 fs/namei.c:2771
do_move_mount_old+0x5d/0xd0 fs/namespace.c:3374
path_mount+0x536/0xb30 fs/namespace.c:3832
do_mount fs/namespace.c:3847 [inline]
__do_sys_mount fs/namespace.c:4057 [inline]
__se_sys_mount+0x27c/0x2d0 fs/namespace.c:4034
__x64_sys_mount+0x67/0x80 fs/namespace.c:4034
x64_sys_call+0x2c84/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888137c98b40 -> 0xffff888119c47cc0

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 29883 Comm: syz.8.7922 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================


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[syzbot]

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