[syzbot] [fs?] possible deadlock in uvcg_extension_bm_controls_store

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3aa1dcaa4f6f Revert "wifi: mt76: Disable napi when removin..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1619d149580000
kernel config: https://syzkaller.appspot.com/x/.config?x=aaf0da806f995318
dashboard link: https://syzkaller.appspot.com/bug?extid=300213c2b5b55c0244f4
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/6f9bf8386a97/disk-3aa1dcaa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/11e9065ece34/vmlinux-3aa1dcaa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0c2427f0862d/bzImage-3aa1dcaa.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+300213...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.1.302/7497 is trying to acquire lock:
ffffffff8f9eb2a8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125

but task is already holding lock:
ffff88803317f470 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff88803317f470 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x238/0x430 fs/configfs/file.c:229

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&p->frag_sem){++++}-{4:4}:
down_write_killable+0xa6/0x240 kernel/locking/rwsem.c:1643
configfs_rmdir+0x3b0/0x950 fs/configfs/dir.c:1534
vfs_rmdir+0x3e6/0x6a0 fs/namei.c:5381
filename_rmdir+0x292/0x520 fs/namei.c:5438
__do_sys_unlinkat fs/namei.c:5613 [inline]
__se_sys_unlinkat+0x71/0x1a0 fs/namei.c:5606
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

-> #2 (&sb->s_type->i_mutex_key#32){++++}-{4:4}:
down_write+0x96/0x200 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+0x406/0x620 fs/namei.c:5276
filename_mkdirat+0x285/0x510 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5327
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/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
tcm_set_name+0x2b/0xd0 drivers/usb/gadget/function/f_tcm.c:2669
function_make+0x1a8/0x360 drivers/usb/gadget/configfs.c:636
configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1360
vfs_mkdir+0x406/0x620 fs/namei.c:5276
filename_mkdirat+0x285/0x510 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5327
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+0x1520/0x2cf0 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
uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x612/0xba0 fs/read_write.c:687
ksys_write+0x150/0x270 fs/read_write.c:739
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 --> &sb->s_type->i_mutex_key#32 --> &p->frag_sem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&p->frag_sem);
lock(&sb->s_type->i_mutex_key#32);
lock(&p->frag_sem);
lock(gadget_subsys.su_mutex);

*** DEADLOCK ***

4 locks held by syz.1.302/7497:
#0: ffff888061692470 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259
#1: ffff88801bf16450 (sb_writers#22){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2733 [inline]
#1: ffff88801bf16450 (sb_writers#22){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
#2: ffff8880783f4480 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x7e/0x430 fs/configfs/file.c:226
#3: ffff88803317f470 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
#3: ffff88803317f470 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x238/0x430 fs/configfs/file.c:229

stack backtrace:
CPU: 0 UID: 0 PID: 7497 Comm: syz.1.302 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
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+0x1520/0x2cf0 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
uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x612/0xba0 fs/read_write.c:687
ksys_write+0x150/0x270 fs/read_write.c:739
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: 0033:0x7f9d8819e0d9
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:00007f9d890b3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9d88425fa0 RCX: 00007f9d8819e0d9
RDX: 0000000000000050 RSI: 0000200000000440 RDI: 0000000000000009
RBP: 00007f9d88235024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9d88426038 R14: 00007f9d88425fa0 R15: 00007fffe7d8ced8
</TASK>


---
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