[syzbot] [usb?] possible deadlock in uvcg_extension_allow_link

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: [email protected]

======================================================
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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