[syzbot] [usb?] possible deadlock in uvcg_extension_allow_link

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 365f9c7a6b81 Merge branches 'for-next/core' and 'for-next/..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=14f3649e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=72c97575381cec47
dashboard link: https://syzkaller.appspot.com/bug?extid=b3410eb576b568216ae5
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10b83632580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15874aea580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eafe0adb7386/disk-365f9c7a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/29422d607579/vmlinux-365f9c7a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/98ca955a8b54/Image-365f9c7a.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b3410e...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.18/4919 is trying to acquire lock:
ffff80008970de48 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_extension_allow_link+0x70/0x1f8 drivers/usb/gadget/function/uvc_configfs.c:1195

but task is already holding lock:
ffff0000f06efa40 (&sb->s_type->i_mutex_key#23){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff0000f06efa40 (&sb->s_type->i_mutex_key#23){+.+.}-{4:4}, at: configfs_symlink+0x394/0xde0 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#23){+.+.}-{4:4}:
down_write+0x50/0xc0 kernel/locking/rwsem.c:1631
inode_lock include/linux/fs.h:1024 [inline]
configfs_depend_item_unlocked+0x154/0x344 fs/configfs/dir.c:1259
usbg_make_tpg+0x230/0x4b4 drivers/usb/gadget/function/f_tcm.c:1686
target_fabric_make_tpg+0x98/0x518 drivers/target/target_core_fabric_configfs.c:939
configfs_mkdir+0x374/0x7d4 fs/configfs/dir.c:1360
vfs_mkdir+0x2dc/0x464 fs/namei.c:5276
filename_mkdirat+0x228/0x3f4 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat fs/namei.c:5327 [inline]
__arm64_sys_mkdirat+0x94/0xb8 fs/namei.c:5327
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

-> #1 (&opts->dep_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
tcm_set_name+0x34/0xd0 drivers/usb/gadget/function/f_tcm.c:2540
function_make+0x18c/0x300 drivers/usb/gadget/configfs.c:636
configfs_mkdir+0x374/0x7d4 fs/configfs/dir.c:1360
vfs_mkdir+0x2dc/0x464 fs/namei.c:5276
filename_mkdirat+0x228/0x3f4 fs/namei.c:5309
__do_sys_mkdirat fs/namei.c:5330 [inline]
__se_sys_mkdirat fs/namei.c:5327 [inline]
__arm64_sys_mkdirat+0x94/0xb8 fs/namei.c:5327
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

-> #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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237
lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
uvcg_extension_allow_link+0x70/0x1f8 drivers/usb/gadget/function/uvc_configfs.c:1195
configfs_symlink+0x478/0xde0 fs/configfs/symlink.c:196
vfs_symlink+0x16c/0x290 fs/namei.c:5660
filename_symlinkat+0x18c/0x328 fs/namei.c:5685
__do_sys_symlinkat fs/namei.c:5705 [inline]
__se_sys_symlinkat fs/namei.c:5700 [inline]
__arm64_sys_symlinkat+0xa8/0xd4 fs/namei.c:5700
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

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.0.18/4919:
#0: ffff0000c38e0450 (sb_writers#11){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:494
#1: ffff0000f06efa40 (&sb->s_type->i_mutex_key#23){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
#1: ffff0000f06efa40 (&sb->s_type->i_mutex_key#23){+.+.}-{4:4}, at: configfs_symlink+0x394/0xde0 fs/configfs/symlink.c:186

stack backtrace:
CPU: 0 UID: 0 PID: 4919 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
dump_stack+0x1c/0x28 lib/dump_stack.c:129
print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2043
check_noncircular+0x158/0x174 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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237
lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
uvcg_extension_allow_link+0x70/0x1f8 drivers/usb/gadget/function/uvc_configfs.c:1195
configfs_symlink+0x478/0xde0 fs/configfs/symlink.c:196
vfs_symlink+0x16c/0x290 fs/namei.c:5660
filename_symlinkat+0x18c/0x328 fs/namei.c:5685
__do_sys_symlinkat fs/namei.c:5705 [inline]
__se_sys_symlinkat fs/namei.c:5700 [inline]
__arm64_sys_symlinkat+0xa8/0xd4 fs/namei.c:5700
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594


---
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