[syzbot] [usb?] possible deadlock in uvc_func_allow_link

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=1198109e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=8c0a48f6c8357c9da819
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1eb5b7aa9ec5/disk-48a5a7ab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/965506e050aa/vmlinux-48a5a7ab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/662778208054/bzImage-48a5a7ab.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 Tainted: G             L     
------------------------------------------------------
syz.9.4116/22505 is trying to acquire lock:
ffffffff901cfe68 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651

but task is already holding lock:
ffff888057290f80 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff888057290f80 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: configfs_symlink+0x3c0/0x11f0 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#28){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
       inode_lock include/linux/fs.h:1024 [inline]
       configfs_depend_item_unlocked+0xf3/0x6a0 fs/configfs/dir.c:1259
       usbg_make_tpg+0x261/0x620 drivers/usb/gadget/function/f_tcm.c:1686
       target_fabric_make_tpg+0xab/0x8c0 drivers/target/target_core_fabric_configfs.c:939
       configfs_mkdir+0x51e/0xb70 fs/configfs/dir.c:1360
       vfs_mkdir+0x361/0x850 fs/namei.c:5276
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5309
       __do_sys_mkdirat fs/namei.c:5330 [inline]
       __se_sys_mkdirat fs/namei.c:5327 [inline]
       __x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5327
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&opts->dep_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       tcm_set_name+0x29/0xb0 drivers/usb/gadget/function/f_tcm.c:2540
       function_make+0x21c/0x3f0 drivers/usb/gadget/configfs.c:636
       configfs_mkdir+0x51e/0xb70 fs/configfs/dir.c:1360
       vfs_mkdir+0x361/0x850 fs/namei.c:5276
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5309
       __do_sys_mkdirat fs/namei.c:5330 [inline]
       __se_sys_mkdirat fs/namei.c:5327 [inline]
       __x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5327
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (gadget_subsys.su_mutex){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
       configfs_symlink+0x540/0x11f0 fs/configfs/symlink.c:196
       vfs_symlink fs/namei.c:5660 [inline]
       vfs_symlink+0x178/0x4d0 fs/namei.c:5639
       filename_symlinkat+0x2a6/0x560 fs/namei.c:5685
       __do_sys_symlink fs/namei.c:5712 [inline]
       __se_sys_symlink fs/namei.c:5708 [inline]
       __x64_sys_symlink+0x79/0xb0 fs/namei.c:5708
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 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#28

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#28);
                               lock(&opts->dep_lock);
                               lock(&sb->s_type->i_mutex_key#28);
  lock(gadget_subsys.su_mutex);

 *** DEADLOCK ***

2 locks held by syz.9.4116/22505:
 #0: ffff88801e3b0450 (sb_writers#17){.+.+}-{0:0}, at: filename_create+0x10d/0x400 fs/namei.c:4948
 #1: ffff888057290f80 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #1: ffff888057290f80 (&sb->s_type->i_mutex_key#28){++++}-{4:4}, at: configfs_symlink+0x3c0/0x11f0 fs/configfs/symlink.c:186

stack backtrace:
CPU: 0 UID: 0 PID: 22505 Comm: syz.9.4116 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 lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
 configfs_symlink+0x540/0x11f0 fs/configfs/symlink.c:196
 vfs_symlink fs/namei.c:5660 [inline]
 vfs_symlink+0x178/0x4d0 fs/namei.c:5639
 filename_symlinkat+0x2a6/0x560 fs/namei.c:5685
 __do_sys_symlink fs/namei.c:5712 [inline]
 __se_sys_symlink fs/namei.c:5708 [inline]
 __x64_sys_symlink+0x79/0xb0 fs/namei.c:5708
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff24159de99
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:00007ff2423d2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007ff241825fa0 RCX: 00007ff24159de99
RDX: 0000000000000000 RSI: 00002000000000c0 RDI: 0000200000000040
RBP: 00007ff241633eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff241826038 R14: 00007ff241825fa0 R15: 00007ffd6dfc08d8
 </TASK>


---
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