[v6.6] possible deadlock in uvc_func_allow_link

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: aa0e49877a2e Linux 6.6.148
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=142233b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=4dd125cbd4c6b9ba7c29
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f83b390cfc1f/disk-aa0e4987.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1d4bdb338edd/vmlinux-aa0e4987.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3f57c1d51ee3/bzImage-aa0e4987.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4dd125...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.5.3172/19077 is trying to acquire lock:
ffffffff8ddf7170 (gadget_subsys.su_mutex){+.+.}-{3:3}, at: uvc_func_allow_link+0x70/0x360 drivers/usb/gadget/function/uvc_configfs.c:3314

but task is already holding lock:
ffff88805f4ea9e0 (&sb->s_type->i_mutex_key#23){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
ffff88805f4ea9e0 (&sb->s_type->i_mutex_key#23){++++}-{3:3}, at: configfs_symlink+0x47a/0xfe0 fs/configfs/symlink.c:192

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&sb->s_type->i_mutex_key#23){++++}-{3:3}:
down_write+0x97/0x200 kernel/locking/rwsem.c:1573
inode_lock include/linux/fs.h:804 [inline]
configfs_depend_item_unlocked+0x157/0x430 fs/configfs/dir.c:1255
usbg_make_tpg+0x1f7/0x580 drivers/usb/gadget/function/f_tcm.c:1341
target_fabric_make_tpg+0xa4/0x6d0 drivers/target/target_core_fabric_configfs.c:939
configfs_mkdir+0x515/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x2a5/0x470 fs/namei.c:4168
do_mkdirat+0x1dc/0x450 fs/namei.c:4191
__do_sys_mkdirat fs/namei.c:4206 [inline]
__se_sys_mkdirat fs/namei.c:4204 [inline]
__x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4204
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&opts->dep_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
tcm_set_name+0x2a/0x90 drivers/usb/gadget/function/f_tcm.c:2188
function_make+0x199/0x350 drivers/usb/gadget/configfs.c:635
configfs_mkdir+0x515/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x2a5/0x470 fs/namei.c:4168
do_mkdirat+0x1dc/0x450 fs/namei.c:4191
__do_sys_mkdirat fs/namei.c:4206 [inline]
__se_sys_mkdirat fs/namei.c:4204 [inline]
__x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4204
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (gadget_subsys.su_mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x37ef/0x7d80 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+0x135/0xc80 kernel/locking/mutex.c:747
uvc_func_allow_link+0x70/0x360 drivers/usb/gadget/function/uvc_configfs.c:3314
configfs_symlink+0x5a5/0xfe0 fs/configfs/symlink.c:202
vfs_symlink+0x138/0x2b0 fs/namei.c:4528
do_symlinkat+0x1ba/0x400 fs/namei.c:4554
__do_sys_symlink fs/namei.c:4575 [inline]
__se_sys_symlink fs/namei.c:4573 [inline]
__x64_sys_symlink+0x7e/0x90 fs/namei.c:4573
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
gadget_subsys.su_mutex --> &opts->dep_lock --> &sb->s_type->i_mutex_key#23

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sb->s_type->i_mutex_key#23);
lock(&opts->dep_lock);
lock(&sb->s_type->i_mutex_key#23);
lock(gadget_subsys.su_mutex);

*** DEADLOCK ***

2 locks held by syz.5.3172/19077:
#0: ffff888019320418 (sb_writers#16){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:412
#1: ffff88805f4ea9e0 (&sb->s_type->i_mutex_key#23){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#1: ffff88805f4ea9e0 (&sb->s_type->i_mutex_key#23){++++}-{3:3}, at: configfs_symlink+0x47a/0xfe0 fs/configfs/symlink.c:192

stack backtrace:
CPU: 0 PID: 19077 Comm: syz.5.3172 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x37ef/0x7d80 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+0x135/0xc80 kernel/locking/mutex.c:747
uvc_func_allow_link+0x70/0x360 drivers/usb/gadget/function/uvc_configfs.c:3314
configfs_symlink+0x5a5/0xfe0 fs/configfs/symlink.c:202
vfs_symlink+0x138/0x2b0 fs/namei.c:4528
do_symlinkat+0x1ba/0x400 fs/namei.c:4554
__do_sys_symlink fs/namei.c:4575 [inline]
__se_sys_symlink fs/namei.c:4573 [inline]
__x64_sys_symlink+0x7e/0x90 fs/namei.c:4573
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f401979e019
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:00007f401a5fe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007f4019a25fa0 RCX: 00007f401979e019
RDX: 0000000000000000 RSI: 0000200000001b00 RDI: 00002000000000c0
RBP: 00007f401983500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4019a26038 R14: 00007f4019a25fa0 R15: 00007ffdf5d52d58
</TASK>


---
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