=========================
WARNING: held lock freed!
syzkaller #0 Not tainted
-------------------------
kworker/0:5/4244 is freeing memory ffff88807c408c40-ffff88807c4097c7, with a lock still held there!
ffff88807c408d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1731 [inline]
ffff88807c408d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_worker+0x31/0xc70 net/mptcp/protocol.c:2527
3 locks held by kworker/0:5/4244:
 #0: ffff888016870938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc9000326fd00 ((work_completion)(&msk->work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
 #2: ffff88807c408d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1731 [inline]
 #2: ffff88807c408d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_worker+0x31/0xc70 net/mptcp/protocol.c:2527

stack backtrace:
CPU: 0 PID: 4244 Comm: kworker/0:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events mptcp_worker
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 print_freed_lock_bug kernel/locking/lockdep.c:6401 [inline]
 debug_check_no_locks_freed+0x2f2/0x3c0 kernel/locking/lockdep.c:6434
 slab_free_hook mm/slub.c:1682 [inline]
 slab_free_freelist_hook+0x76/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kmem_cache_free+0x8f/0x210 mm/slub.c:3520
 sk_prot_free net/core/sock.c:1903 [inline]
 __sk_destruct+0x569/0x840 net/core/sock.c:1991
 sock_put include/net/sock.h:1976 [inline]
 __mptcp_destroy_sock+0x5c1/0x720 net/mptcp/protocol.c:2795
 mptcp_worker+0x878/0xc70 net/mptcp/protocol.c:2553
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 4244 at lib/refcount.c:28 refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 4244 Comm: kworker/0:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events mptcp_worker
RIP: 0010:refcount_warn_saturate+0x11b/0x1a0 lib/refcount.c:28
Code: 09 01 48 c7 c7 c0 a8 59 8a e8 31 c1 c3 05 0f 0b eb c4 e8 48 e5 9c fd c6 05 9e 11 7b 09 01 48 c7 c7 20 a9 59 8a e8 15 c1 c3 05 <0f> 0b eb a8 e8 2c e5 9c fd c6 05 7f 11 7b 09 01 48 c7 c7 60 a8 59
RSP: 0018:ffffc9000326fc28 EFLAGS: 00010246
RAX: 9c144039d6085a00 RBX: 0000000000000003 RCX: ffff88801ff00000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc9000326fdb8 R08: dffffc0000000000 R09: ffffed10172067b0
R10: ffffed10172067b0 R11: 1ffff110172067af R12: dffffc0000000000
R13: ffff8880224ebb18 R14: 0000000000000003 R15: ffff8880b903f008
FS:  0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8e0f52a568 CR3: 000000005a636000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>