======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.4.521/7882 is trying to acquire lock:
ffffffff901ad880 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_streaming_class_drop_link+0x70/0x540 drivers/usb/gadget/function/uvc_configfs.c:3502

but task is already holding lock:
ffff888070ea4258 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
ffff888070ea4258 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: vfs_unlink+0xd4/0x720 fs/namei.c:5653

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&sb->s_type->i_mutex_key#28){++++}-{4:4}:
       down_write+0x35/0x50 kernel/locking/rwsem.c:1631
       inode_lock include/linux/fs.h:1027 [inline]
       configfs_depend_item_unlocked+0x153/0x420 fs/configfs/dir.c:1268
       usbg_make_tpg+0x1e0/0x550 drivers/usb/gadget/function/f_tcm.c:1692
       target_fabric_make_tpg+0xa8/0x6d0 drivers/target/target_core_fabric_configfs.c:947
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x417/0x670 fs/namei.c:5428
       filename_mkdirat+0x288/0x560 fs/namei.c:5461
       __do_sys_mkdirat fs/namei.c:5482 [inline]
       __se_sys_mkdirat+0x35/0x150 fs/namei.c:5479
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (tpg_instances_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x55/0x1d0 kernel/locking/rtmutex_api.c:580
       tcm_alloc_inst+0x65/0x1a0 drivers/usb/gadget/function/f_tcm.c:2687
       try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
       usb_get_function_instance+0xe3/0x2f0 drivers/usb/gadget/functions.c:44
       function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x417/0x670 fs/namei.c:5428
       filename_mkdirat+0x288/0x560 fs/namei.c:5461
       __do_sys_mkdirat fs/namei.c:5482 [inline]
       __se_sys_mkdirat+0x35/0x150 fs/namei.c:5479
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (func_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x55/0x1d0 kernel/locking/rtmutex_api.c:580
       try_get_usb_function_instance drivers/usb/gadget/functions.c:18 [inline]
       usb_get_function_instance+0x2e/0x2f0 drivers/usb/gadget/functions.c:44
       function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x417/0x670 fs/namei.c:5428
       filename_mkdirat+0x288/0x560 fs/namei.c:5461
       __do_sys_mkdirat fs/namei.c:5482 [inline]
       __se_sys_mkdirat+0x35/0x150 fs/namei.c:5479
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (gadget_subsys.su_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x55/0x1d0 kernel/locking/rtmutex_api.c:580
       uvcg_streaming_class_drop_link+0x70/0x540 drivers/usb/gadget/function/uvc_configfs.c:3502
       configfs_unlink+0x44f/0x6b0 fs/configfs/symlink.c:258
       vfs_unlink+0x279/0x720 fs/namei.c:5667
       filename_unlinkat+0x297/0x5c0 fs/namei.c:5737
       __do_sys_unlink fs/namei.c:5772 [inline]
       __se_sys_unlink+0x2e/0x140 fs/namei.c:5769
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  gadget_subsys.su_mutex --> tpg_instances_lock --> &sb->s_type->i_mutex_key#28

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#28);
                               lock(tpg_instances_lock);
                               lock(&sb->s_type->i_mutex_key#28);
  lock(gadget_subsys.su_mutex);

 *** DEADLOCK ***

locks held by syz.4.521/7882: 3, on CPU#1:
 #0: ffff88801ef46528 (sb_writers#17){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:531
 #1: ffff888045cee2c8 (&default_group_class[depth - 1]#9/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1072 [inline]
 #1: ffff888045cee2c8 (&default_group_class[depth - 1]#9/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2924 [inline]
 #1: ffff888045cee2c8 (&default_group_class[depth - 1]#9/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2948 [inline]
 #1: ffff888045cee2c8 (&default_group_class[depth - 1]#9/1){+.+.}-{4:4}, at: filename_unlinkat+0x198/0x5c0 fs/namei.c:5718
 #2: ffff888070ea4258 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
 #2: ffff888070ea4258 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: vfs_unlink+0xd4/0x720 fs/namei.c:5653

stack backtrace:
CPU: 1 UID: 0 PID: 7882 Comm: syz.4.521 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
 mutex_lock_nested+0x55/0x1d0 kernel/locking/rtmutex_api.c:580
 uvcg_streaming_class_drop_link+0x70/0x540 drivers/usb/gadget/function/uvc_configfs.c:3502
 configfs_unlink+0x44f/0x6b0 fs/configfs/symlink.c:258
 vfs_unlink+0x279/0x720 fs/namei.c:5667
 filename_unlinkat+0x297/0x5c0 fs/namei.c:5737
 __do_sys_unlink fs/namei.c:5772 [inline]
 __se_sys_unlink+0x2e/0x140 fs/namei.c:5769
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8421a194d9
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:00007f841fc5e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 00007f8421c95fa0 RCX: 00007f8421a194d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000500
RBP: 00007f8421aa804e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8421c96038 R14: 00007f8421c95fa0 R15: 00007fff1cb2cea8
 </TASK>