[moderation] [fs?] KCSAN: data-race in __lookup_mnt / umount_tree (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 795c58e4c7fc Merge tag 'trace-v6.10-rc6' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e4b2e1980000
kernel config: https://syzkaller.appspot.com/x/.config?x=5b9537cd00be479e
dashboard link: https://syzkaller.appspot.com/bug?extid=e12a5cdf6763ceb240a6
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/3d1d205c1fdf/disk-795c58e4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/641c78d42b7a/vmlinux-795c58e4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/45ecf25d8ba3/bzImage-795c58e4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e12a5c...@syzkaller.appspotmail.com

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

write to 0xffff888104103218 of 8 bytes by task 4547 on cpu 1:
unhash_mnt fs/namespace.c:892 [inline]
umount_mnt fs/namespace.c:906 [inline]
umount_tree+0x63f/0x910 fs/namespace.c:1673
path_umount+0x98a/0xa10 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
x64_sys_call+0x3af/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:167
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 0xffff888104103218 of 8 bytes by task 4548 on cpu 0:
__lookup_mnt+0xa0/0xf0 fs/namespace.c:701
__follow_mount_rcu fs/namei.c:1506 [inline]
handle_mounts fs/namei.c:1536 [inline]
step_into+0x434/0x810 fs/namei.c:1842
walk_component fs/namei.c:2010 [inline]
link_path_walk+0x49d/0x810 fs/namei.c:2331
path_lookupat+0x72/0x2b0 fs/namei.c:2492
filename_lookup+0x127/0x300 fs/namei.c:2522
user_path_at_empty+0x42/0x120 fs/namei.c:2929
user_path_at include/linux/namei.h:58 [inline]
ksys_umount fs/namespace.c:1916 [inline]
__do_sys_umount fs/namespace.c:1924 [inline]
__se_sys_umount fs/namespace.c:1922 [inline]
__x64_sys_umount+0x88/0xe0 fs/namespace.c:1922
x64_sys_call+0x3af/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:167
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: 0xffff888108806b40 -> 0xffff888108806d80

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4548 Comm: syz.4.338 Not tainted 6.10.0-rc6-syzkaller-00069-g795c58e4c7fc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
==================================================================


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