[syzbot] [usb?] possible deadlock in mdc800_device_open

[syzbot] [usb?] possible deadlock in mdc800_device_open

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    dcb68831eac7 Merge tag 'block-7.2-20260815' of git://git.k..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1667ea25580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2ca5f2f2c4197664
dashboard link: https://syzkaller.appspot.com/bug?extid=023b30ebfe0dc4bcfafe
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15fe2679580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=167fda79580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2f9d6a54222e/disk-dcb68831.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0b52c510b447/vmlinux-dcb68831.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f8d408f8474e/bzImage-dcb68831.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+023b30ebfe0dc4bcfafe@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor372/5624 is trying to acquire lock:
ffff888029dc0218 (&mdc800->io_lock){+.+.}-{4:4}, at: mdc800_device_open+0x2e/0x470 drivers/usb/image/mdc800.c:611

but task is already holding lock:
ffffffff8f8e0868 (minor_rwsem#2){++++}-{4:4}, at: usb_open+0x30/0x1e0 drivers/usb/core/file.c:38

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (minor_rwsem#2){++++}-{4:4}:
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       usb_register_dev+0x142/0x5e0 drivers/usb/core/file.c:134
       mdc800_usb_probe+0xf96/0x18c0 drivers/usb/image/mdc800.c:485
       usb_probe_interface+0x653/0xc60 drivers/usb/core/driver.c:396
       call_driver_probe drivers/base/dd.c:-1 [inline]
       really_probe+0x254/0xae0 drivers/base/dd.c:706
       __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
       driver_probe_device+0x4f/0x240 drivers/base/dd.c:898
       __device_attach_driver+0x270/0x410 drivers/base/dd.c:1026
       bus_for_each_drv+0x258/0x2f0 drivers/base/bus.c:500
       __device_attach+0x2c4/0x450 drivers/base/dd.c:1098
       device_initial_probe+0xa1/0xd0 drivers/base/dd.c:1153
       bus_probe_device+0x12a/0x220 drivers/base/bus.c:620
       device_add+0x7d7/0xb80 drivers/base/core.c:3772
       usb_set_configuration+0x1ad8/0x2180 drivers/usb/core/message.c:2268
       usb_generic_driver_probe+0x8d/0x150 drivers/usb/core/generic.c:250
       usb_probe_device+0x1c3/0x3b0 drivers/usb/core/driver.c:291
       call_driver_probe drivers/base/dd.c:-1 [inline]
       really_probe+0x254/0xae0 drivers/base/dd.c:706
       __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
       driver_probe_device+0x4f/0x240 drivers/base/dd.c:898
       __device_attach_driver+0x270/0x410 drivers/base/dd.c:1026
       bus_for_each_drv+0x258/0x2f0 drivers/base/bus.c:500
       __device_attach+0x2c4/0x450 drivers/base/dd.c:1098
       device_initial_probe+0xa1/0xd0 drivers/base/dd.c:1153
       bus_probe_device+0x12a/0x220 drivers/base/bus.c:620
       device_add+0x7d7/0xb80 drivers/base/core.c:3772
       usb_new_device+0x9aa/0x1690 drivers/usb/core/hub.c:2703
       hub_port_connect drivers/usb/core/hub.c:5575 [inline]
       hub_port_connect_change drivers/usb/core/hub.c:5715 [inline]
       port_event drivers/usb/core/hub.c:5879 [inline]
       hub_event+0x28e8/0x4d30 drivers/usb/core/hub.c:5961
       process_one_work kernel/workqueue.c:3322 [inline]
       process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&mdc800->io_lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       mdc800_device_open+0x2e/0x470 drivers/usb/image/mdc800.c:611
       usb_open+0x156/0x1e0 drivers/usb/core/file.c:47
       chrdev_open+0x4d9/0x600 fs/char_dev.c:411
       do_dentry_open+0x816/0x1380 fs/open.c:947
       vfs_open+0x3b/0x340 fs/open.c:1052
       do_open fs/namei.c:4700 [inline]
       path_openat+0x2e44/0x3830 fs/namei.c:4863
       do_file_open+0x23e/0x4a0 fs/namei.c:4892
       do_sys_openat2+0x115/0x200 fs/open.c:1368
       do_sys_open fs/open.c:1374 [inline]
       __do_sys_openat fs/open.c:1390 [inline]
       __se_sys_openat fs/open.c:1385 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1385
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(minor_rwsem#2);
                               lock(&mdc800->io_lock);
                               lock(minor_rwsem#2);
  lock(&mdc800->io_lock);

 *** DEADLOCK ***

1 lock held by syz-executor372/5624:
 #0: ffffffff8f8e0868 (minor_rwsem#2){++++}-{4:4}, at: usb_open+0x30/0x1e0 drivers/usb/core/file.c:38

stack backtrace:
CPU: 0 UID: 0 PID: 5624 Comm: syz-executor372 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 mdc800_device_open+0x2e/0x470 drivers/usb/image/mdc800.c:611
 usb_open+0x156/0x1e0 drivers/usb/core/file.c:47
 chrdev_open+0x4d9/0x600 fs/char_dev.c:411
 do_dentry_open+0x816/0x1380 fs/open.c:947
 vfs_open+0x3b/0x340 fs/open.c:1052
 do_open fs/namei.c:4700 [inline]
 path_openat+0x2e44/0x3830 fs/namei.c:4863
 do_file_open+0x23e/0x4a0 fs/namei.c:4892
 do_sys_openat2+0x115/0x200 fs/open.c:1368
 do_sys_open fs/open.c:1374 [inline]
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1385
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2ac746d097
Code: 48 89 fa 4c 89 df e8 48 1f 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffd29cf7470 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000055557962c400 RCX: 00007f2ac746d097
RDX: 0000000000000002 RSI: 00007ffd29cf7510 RDI: ffffffffffffff9c
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007ffd29cf7708
R13: 431bde82d7b634db R14: 00007f2ac74eec40 R15: 0000000000000002
 </TASK>


---
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