[syzbot] [usb?] possible deadlock in uvcg_streaming_header_allow_link

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 48a5a7ab8d6a Merge tag 'v7.2-rc4-smb3-client-fixes' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16bfd746580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
dashboard link: https://syzkaller.appspot.com/bug?extid=ed4b9a6a61280b24d9c3
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=101fe09e580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=100886b9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d0d4e9604889/disk-48a5a7ab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d0017d0f35e6/vmlinux-48a5a7ab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/81888db0a443/bzImage-48a5a7ab.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ed4b9a...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.18/5837 is trying to acquire lock:
ffffffff8ef6f000 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_streaming_header_allow_link+0x75/0x4d0 drivers/usb/gadget/function/uvc_configfs.c:1750

but task is already holding lock:
ffff88803cdb6830 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff88803cdb6830 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: configfs_symlink+0x3af/0x1030 fs/configfs/symlink.c:186

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}:
down_write+0x3a/0x50 kernel/locking/rwsem.c:1631
inode_lock include/linux/fs.h:1024 [inline]
configfs_depend_item_unlocked+0x153/0x420 fs/configfs/dir.c:1259
usbg_make_tpg+0x1f6/0x590 drivers/usb/gadget/function/f_tcm.c:1686
target_fabric_make_tpg+0xa8/0x6d0 drivers/target/target_core_fabric_configfs.c:939
configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x402/0x620 fs/namei.c:5276
filename_mkdirat+0x289/0x520 fs/namei.c:5309
__do_sys_mkdir fs/namei.c:5336 [inline]
__se_sys_mkdir+0x34/0x150 fs/namei.c:5333
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

-> #1 (&opts->dep_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
tcm_set_name+0x2b/0xd0 drivers/usb/gadget/function/f_tcm.c:2540
function_make+0x1a8/0x360 drivers/usb/gadget/configfs.c:636
configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x402/0x620 fs/namei.c:5276
filename_mkdirat+0x289/0x520 fs/namei.c:5309
__do_sys_mkdir fs/namei.c:5336 [inline]
__se_sys_mkdir+0x34/0x150 fs/namei.c:5333
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

-> #0 (gadget_subsys.su_mutex){+.+.}-{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+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
uvcg_streaming_header_allow_link+0x75/0x4d0 drivers/usb/gadget/function/uvc_configfs.c:1750
configfs_symlink+0x59a/0x1030 fs/configfs/symlink.c:196
vfs_symlink+0x18b/0x330 fs/namei.c:5660
filename_symlinkat+0x1cd/0x420 fs/namei.c:5685
__do_sys_symlink fs/namei.c:5712 [inline]
__se_sys_symlink+0x4d/0x2b0 fs/namei.c:5708
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:

Chain exists of:
gadget_subsys.su_mutex --> &opts->dep_lock --> &sb->s_type->i_mutex_key#24

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sb->s_type->i_mutex_key#24);
lock(&opts->dep_lock);
lock(&sb->s_type->i_mutex_key#24);
lock(gadget_subsys.su_mutex);

*** DEADLOCK ***

2 locks held by syz.0.18/5837:
#0: ffff88801bf26500 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:494
#1: ffff88803cdb6830 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
#1: ffff88803cdb6830 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: configfs_symlink+0x3af/0x1030 fs/configfs/symlink.c:186

stack backtrace:
CPU: 1 UID: 0 PID: 5837 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
uvcg_streaming_header_allow_link+0x75/0x4d0 drivers/usb/gadget/function/uvc_configfs.c:1750
configfs_symlink+0x59a/0x1030 fs/configfs/symlink.c:196
vfs_symlink+0x18b/0x330 fs/namei.c:5660
filename_symlinkat+0x1cd/0x420 fs/namei.c:5685
__do_sys_symlink fs/namei.c:5712 [inline]
__se_sys_symlink+0x4d/0x2b0 fs/namei.c:5708
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: 0033:0x7f02ea0fde99
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:00007ffed3700ec8 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007f02ea385fa0 RCX: 00007f02ea0fde99
RDX: 0000000000000000 RSI: 0000200000001500 RDI: 0000200000001400
RBP: 00007f02ea193eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f02ea385fac R14: 00007f02ea385fa0 R15: 00007f02ea385fa0
</TASK>


---
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