[moderation] [fs?] KCSAN: data-race in __lookup_mnt / umount_tree (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9b6de136b5f0 Merge tag 'loongarch-fixes-6.7-1' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16eb14a4e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=8c1151391aefc0c3
dashboard link: https://syzkaller.appspot.com/bug?extid=13bd49aa14031230b4a9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [bra...@kernel.org 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/66e487a84769/disk-9b6de136.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/68701b15ec8c/vmlinux-9b6de136.xz
kernel image: https://storage.googleapis.com/syzbot-assets/78c7cba56794/bzImage-9b6de136.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+13bd49...@syzkaller.appspotmail.com

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

write to 0xffff888135a3e510 of 8 bytes by task 3129 on cpu 0:
unhash_mnt fs/namespace.c:905 [inline]
umount_mnt fs/namespace.c:920 [inline]
umount_tree+0x574/0x860 fs/namespace.c:1675
path_umount+0x928/0x9a0 fs/namespace.c:1896
ksys_umount fs/namespace.c:1919 [inline]
__do_sys_umount fs/namespace.c:1924 [inline]
__se_sys_umount fs/namespace.c:1922 [inline]
__x64_sys_umount+0xb9/0xe0 fs/namespace.c:1922
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888135a3e510 of 8 bytes by task 15045 on cpu 1:
__lookup_mnt+0x83/0xf0 fs/namespace.c:696
__follow_mount_rcu fs/namei.c:1508 [inline]
handle_mounts fs/namei.c:1538 [inline]
step_into+0x430/0x800 fs/namei.c:1840
walk_component fs/namei.c:2008 [inline]
link_path_walk+0x4d8/0x7e0 fs/namei.c:2329
path_parentat fs/namei.c:2530 [inline]
__filename_parentat+0x13b/0x3c0 fs/namei.c:2554
filename_parentat fs/namei.c:2572 [inline]
do_renameat2+0x32e/0xa40 fs/namei.c:4912
__do_sys_rename fs/namei.c:5042 [inline]
__se_sys_rename fs/namei.c:5040 [inline]
__x64_sys_rename+0x5c/0x70 fs/namei.c:5040
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0xffff8881330dcc80 -> 0xffff888135a3e500

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15045 Comm: udevd Not tainted 6.7.0-rc2-syzkaller-00029-g9b6de136b5f0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
==================================================================


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[syzbot]

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