possible deadlock in uvc_func_allow_link

Status: upstream: reported C repro on 2026/07/29 00:09
Subsystems: usb fs
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+8c0a48f6c8357c9da819@syzkaller.appspotmail.com
First crash: 95d, last: 8d06h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
f48f7978 repro-c Reproduced: ✅ ❓ possible deadlock in uvc_func_allow_link 2026/10/20 07:50 2026/10/20 07:50 2026/10/20 09:17 21286ae2
a10caeb3 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in uvc_func_allow_link 2026/07/26 01:14 2026/07/26 01:14 2026/07/26 01:17 492bab15
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [usb?] possible deadlock in uvc_func_allow_link 0 (2) 2026/10/20 09:32
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 possible deadlock in uvc_func_allow_link 4 1 85d 85d 0/2 upstream: reported on 2026/08/04 08:30
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/10/20 09:17 14m retest repro git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git f47d223627f80cb7a1eb14c585fe6cb35de5e984 report job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor238/6025 is trying to acquire lock:
ffffffff914019a8 (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:
ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: configfs_symlink+0x452/0x1340 fs/configfs/symlink.c:201

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       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:1268
       usbg_make_tpg+0x251/0x610 drivers/usb/gadget/function/f_tcm.c:1692
       target_fabric_make_tpg+0xab/0x8c0 drivers/target/target_core_fabric_configfs.c:947
       configfs_mkdir+0x525/0xd40 fs/configfs/dir.c:1369
       vfs_mkdir+0x364/0x850 fs/namei.c:5420
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
       __do_sys_mkdir fs/namei.c:5480 [inline]
       __se_sys_mkdir fs/namei.c:5477 [inline]
       __x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (tpg_instances_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1c20 kernel/locking/mutex.c:821
       tcm_alloc_inst+0x5f/0x1e0 drivers/usb/gadget/function/f_tcm.c:2687
       try_get_usb_function_instance+0x136/0x1f0 drivers/usb/gadget/functions.c:28
       usb_get_function_instance+0x16/0x70 drivers/usb/gadget/functions.c:44
       function_make+0x18c/0x3f0 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x525/0xd40 fs/configfs/dir.c:1369
       vfs_mkdir+0x364/0x850 fs/namei.c:5420
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
       __do_sys_mkdir fs/namei.c:5480 [inline]
       __se_sys_mkdir fs/namei.c:5477 [inline]
       __x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (func_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1c20 kernel/locking/mutex.c:821
       try_get_usb_function_instance+0x26/0x1f0 drivers/usb/gadget/functions.c:18
       usb_get_function_instance+0x16/0x70 drivers/usb/gadget/functions.c:44
       function_make+0x18c/0x3f0 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x525/0xd40 fs/configfs/dir.c:1369
       vfs_mkdir+0x364/0x850 fs/namei.c:5420
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
       __do_sys_mkdir fs/namei.c:5480 [inline]
       __se_sys_mkdir fs/namei.c:5477 [inline]
       __x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (gadget_subsys.su_mutex){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1c20 kernel/locking/mutex.c:821
       uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
       configfs_symlink+0x695/0x1340 fs/configfs/symlink.c:211
       vfs_symlink fs/namei.c:5804 [inline]
       vfs_symlink+0x178/0x4d0 fs/namei.c:5783
       filename_symlinkat+0x2a6/0x560 fs/namei.c:5829
       __do_sys_symlink fs/namei.c:5856 [inline]
       __se_sys_symlink fs/namei.c:5852 [inline]
       __x64_sys_symlink+0x79/0xb0 fs/namei.c:5852
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  gadget_subsys.su_mutex --> tpg_instances_lock --> &sb->s_type->i_mutex_key#25

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#25);
                               lock(tpg_instances_lock);
                               lock(&sb->s_type->i_mutex_key#25);
  lock(gadget_subsys.su_mutex);

 *** DEADLOCK ***

locks held by syz-executor238/6025: 2, last CPU#3:
 #0: ffff888025b44460 (sb_writers#13){.+.+}-{0:0}, at: filename_create+0x10d/0x400 fs/namei.c:5095
 #1: ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #1: ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: configfs_symlink+0x452/0x1340 fs/configfs/symlink.c:201

stack backtrace:
CPU: 3 UID: 0 PID: 6025 Comm: syz-executor238 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
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+0x178/0x1be kernel/locking/lockdep.c:2087
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x1528/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1c20 kernel/locking/mutex.c:821
 uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
 configfs_symlink+0x695/0x1340 fs/configfs/symlink.c:211
 vfs_symlink fs/namei.c:5804 [inline]
 vfs_symlink+0x178/0x4d0 fs/namei.c:5783
 filename_symlinkat+0x2a6/0x560 fs/namei.c:5829
 __do_sys_symlink fs/namei.c:5856 [inline]
 __se_sys_symlink fs/namei.c:5852 [inline]
 __x64_sys_symlink+0x79/0xb0 fs/namei.c:5852
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f17e04c5357
Code: 77 01 c3 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 b8 58 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffdfd785e48 EFLAGS: 00000206 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007f17e051e1e8 RCX: 00007f17e04c5357
RDX: 0000000000000000 RSI: 00007f17e051e170 RDI: 00007f17e051e1e8
RBP: 00007f17e051e300 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 00007f17e051e250
R13: 00007f17e051e298 R14: 00007f17e051e2d8 R15: 00007f17e051e1b0
 </TASK>

Crashes (19):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/20 09:32 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git f47d223627f8 05b26a28 .config console log report C ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/07/25 03:09 upstream 48a5a7ab8d6a 05b26a28 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in uvc_func_allow_link
2026/07/25 02:14 upstream 48a5a7ab8d6a 05b26a28 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in uvc_func_allow_link
2026/10/19 01:15 upstream a0ff06b3a7bd 432c0077 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/08/22 08:43 upstream 818bebeb63dd 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/08/21 16:36 upstream 818bebeb63dd 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/08/20 07:31 upstream a4ff2be345d0 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/08/18 21:33 upstream 0f23d56f17fd 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/07/24 20:40 upstream 48a5a7ab8d6a 4a865b71 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/07/24 20:40 upstream 48a5a7ab8d6a 4a865b71 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream possible deadlock in uvc_func_allow_link
2026/08/29 01:58 upstream 548e7bcd0c54 2f52988a .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvc_func_allow_link
2026/08/24 06:22 upstream 388b607d107c 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvc_func_allow_link
2026/08/13 06:43 upstream 3d6d817622b0 359b2492 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvc_func_allow_link
2026/08/07 18:42 upstream f9a2394a2348 e4ef95d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvc_func_allow_link
2026/08/07 18:42 upstream f9a2394a2348 e4ef95d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvc_func_allow_link
2026/08/24 06:05 linux-next 903c1cf6dff9 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root possible deadlock in uvc_func_allow_link
2026/08/17 19:42 linux-next 4477a78374a5 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce possible deadlock in uvc_func_allow_link
2026/08/17 19:41 linux-next 4477a78374a5 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce possible deadlock in uvc_func_allow_link
2026/07/25 02:30 linux-next cc2b5f627e8c 05b26a28 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce possible deadlock in uvc_func_allow_link
* Struck through repros no longer work on HEAD.