[syzbot] [net?] KCSAN: data-race in l2tp_tunnel_del_work / sk_common_release (7)

Hello,

syzbot found the following issue on:

HEAD commit:    3609fa95fb0f Merge tag 'devicetree-fixes-for-6.19-2' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17de2e9a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=7312e82745f7fa2526db
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3018b7ea95aa/disk-3609fa95.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b7f25f6e87af/vmlinux-3609fa95.xz
kernel image: https://storage.googleapis.com/syzbot-assets/13d7f9c6c13e/bzImage-3609fa95.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7312e82745f7fa2526db@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in l2tp_tunnel_del_work / sk_common_release

write to 0xffff88811bce50e0 of 8 bytes by task 10132 on cpu 1:
 sk_set_socket include/net/sock.h:2092 [inline]
 sock_orphan include/net/sock.h:2118 [inline]
 sk_common_release+0xae/0x230 net/core/sock.c:4003
 udp_lib_close+0x15/0x20 include/net/udp.h:325
 inet_release+0xce/0xf0 net/ipv4/af_inet.c:437
 __sock_release net/socket.c:662 [inline]
 sock_close+0x6b/0x150 net/socket.c:1455
 __fput+0x29b/0x650 fs/file_table.c:468
 ____fput+0x1c/0x30 fs/file_table.c:496
 task_work_run+0x131/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
 exit_to_user_mode_loop+0x1fe/0x740 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x1dd/0x2b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811bce50e0 of 8 bytes by task 6117 on cpu 0:
 l2tp_tunnel_del_work+0x2f/0x1a0 net/l2tp/l2tp_core.c:1418
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x582/0x770 kernel/workqueue.c:3421
 kthread+0x489/0x510 kernel/kthread.c:463
 ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0xffff88811b477a80 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 6117 Comm: kworker/u8:55 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: l2tp l2tp_tunnel_del_work
==================================================================


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