[v6.6] possible deadlock in vmci_qp_broker_detach

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8cee53b8eaeb Linux 6.6.134
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=163782d2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=0fe833fa28bba14eb477
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4c0eb6df7b4a/disk-8cee53b8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/38626ee912e4/vmlinux-8cee53b8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/646a84f3433a/bzImage-8cee53b8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0fe833...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.6.2904/17384 is trying to acquire lock:
ffffffff8da32e18 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

but task is already holding lock:
ffffffff8da32e18 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(qp_broker_list.mutex);
lock(qp_broker_list.mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by syz.6.2904/17384:
#0: ffffffff8da32e18 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

stack backtrace:
CPU: 0 PID: 17384 Comm: syz.6.2904 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain kernel/locking/lockdep.c:3856 [inline]
__lock_acquire+0x5dbc/0x7d40 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x136/0xcc0 kernel/locking/mutex.c:747
vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095
ctx_free_ctx drivers/misc/vmw_vmci/vmci_context.c:444 [inline]
kref_put include/linux/kref.h:65 [inline]
vmci_ctx_put+0x62d/0xc10 drivers/misc/vmw_vmci/vmci_context.c:497
vmci_ctx_enqueue_datagram+0x3ab/0x420 drivers/misc/vmw_vmci/vmci_context.c:360
dg_dispatch_as_host drivers/misc/vmw_vmci/vmci_datagram.c:276 [inline]
vmci_datagram_dispatch+0x44d/0xc60 drivers/misc/vmw_vmci/vmci_datagram.c:340
qp_notify_peer drivers/misc/vmw_vmci/vmci_queue_pair.c:1481 [inline]
vmci_qp_broker_detach+0x8d7/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2188
ctx_free_ctx drivers/misc/vmw_vmci/vmci_context.c:444 [inline]
kref_put include/linux/kref.h:65 [inline]
vmci_ctx_put+0x62d/0xc10 drivers/misc/vmw_vmci/vmci_context.c:497
vmci_host_close+0x9b/0x160 drivers/misc/vmw_vmci/vmci_host.c:143
__fput+0x234/0x970 fs/file_table.c:384
task_work_run+0x1d4/0x260 kernel/task_work.c:245
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f2479b9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2477dd5028 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f2479e16090 RCX: 00007f2479b9c819
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000005
RBP: 00007f2479c32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2479e16128 R14: 00007f2479e16090 R15: 00007fff55617e38
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 9760bf04666d Linux 6.6.135
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=127f0836580000

kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=0fe833fa28bba14eb477
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=103effca580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167754ce580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a685913d05a7/disk-9760bf04.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a3c1d21d4bca/vmlinux-9760bf04.xz
kernel image: https://storage.googleapis.com/syzbot-assets/09178887ef0d/bzImage-9760bf04.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0fe833...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------

syz.0.78/6202 is trying to acquire lock:
ffffffff8da32e58 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

but task is already holding lock:

ffffffff8da32e58 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(qp_broker_list.mutex);
lock(qp_broker_list.mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by syz.0.78/6202:
#0: ffffffff8da32e58 (qp_broker_list.mutex){+.+.}-{3:3}, at: vmci_qp_broker_detach+0x118/0xf10 drivers/misc/vmw_vmci/vmci_queue_pair.c:2095

stack backtrace:
CPU: 1 PID: 6202 Comm: syz.0.78 Not tainted syzkaller #0

RIP: 0033:0x7f7e8cd9c819

Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f7e8dccd028 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f7e8d016090 RCX: 00007f7e8cd9c819

RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000005

RBP: 00007f7e8ce32c91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007f7e8d016128 R14: 00007f7e8d016090 R15: 00007fffa9ea6138
</TASK>


---
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