possible deadlock in tcm_register_callback

Status: upstream: reported on 2026/08/10 00:13
Subsystems: usb
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+642d0d809d2c72babdd2@syzkaller.appspotmail.com
First crash: 18d, last: 3d11h
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
84a1b345 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in tcm_register_callback 2026/08/12 11:18 2026/08/12 11:18 2026/08/12 11:20 f8d35649
9a41b2f6 repro-c Reproduced: ✅ ❓ possible deadlock in tcm_register_callback 2026/08/11 16:59 2026/08/11 23:21 2026/08/12 00:18 f8d35649
1d1a1213 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in tcm_register_callback 2026/08/09 06:42 2026/08/09 06:42 2026/08/09 07:32 5d63f80b
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [usb?] possible deadlock in tcm_register_callback 0 (1) 2026/08/10 00:13
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in tcm_register_callback 4 1 5d09h 5d09h 0/3 upstream: reported on 2026/08/17 21:23
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/08/12 11:18 7h33m nogikh@google.com upstream report job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.91/6209 is trying to acquire lock:
ffff888062b24d10 (&opts->dep_lock){+.+.}-{4:4}, at: tcm_register_callback+0x20/0x70 drivers/usb/gadget/function/f_tcm.c:2625

but task is already holding lock:
ffff88802a5c6c68 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff88802a5c6c68 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x23b/0x430 fs/configfs/file.c:229

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&p->frag_sem){++++}-{4:4}:
       down_write_killable+0x4a/0x80 kernel/locking/rwsem.c:1643
       configfs_rmdir+0x3b0/0x950 fs/configfs/dir.c:1534
       vfs_rmdir+0x3e9/0x6b0 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

-> #1 (&sb->s_type->i_mutex_key#24){++++}-{4:4}:
       down_write+0x3a/0x50 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+0x402/0x620 fs/namei.c:5276
       filename_mkdirat+0x289/0x520 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 (&opts->dep_lock){+.+.}-{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+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       tcm_register_callback+0x20/0x70 drivers/usb/gadget/function/f_tcm.c:2625
       usbg_attach drivers/usb/gadget/function/f_tcm.c:2649 [inline]
       usbg_enable_tpg+0x73/0x120 drivers/usb/gadget/function/f_tcm.c:1825
       target_tpg_enable+0x2e5/0x590 drivers/target/target_core_tpg.c:481
       target_fabric_tpg_base_enable_store+0x122/0x1c0 drivers/target/target_core_fabric_configfs.c:840
       flush_write_buffer fs/configfs/file.c:207 [inline]
       configfs_write_iter+0x33a/0x430 fs/configfs/file.c:229
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x61e/0xbb0 fs/read_write.c:687
       ksys_write+0x156/0x270 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:
  &opts->dep_lock --> &sb->s_type->i_mutex_key#24 --> &p->frag_sem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&p->frag_sem);
                               lock(&sb->s_type->i_mutex_key#24);
                               lock(&p->frag_sem);
  lock(&opts->dep_lock);

 *** DEADLOCK ***

4 locks held by syz.0.91/6209:
 #0: ffff888033538d28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88801cff8500 (sb_writers#12){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2733 [inline]
 #1: ffff88801cff8500 (sb_writers#12){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff8880335fc878 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x81/0x430 fs/configfs/file.c:226
 #3: ffff88802a5c6c68 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
 #3: ffff88802a5c6c68 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x23b/0x430 fs/configfs/file.c:229

stack backtrace:
CPU: 0 UID: 0 PID: 6209 Comm: syz.0.91 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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+0x1520/0x2ce0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
 mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
 tcm_register_callback+0x20/0x70 drivers/usb/gadget/function/f_tcm.c:2625
 usbg_attach drivers/usb/gadget/function/f_tcm.c:2649 [inline]
 usbg_enable_tpg+0x73/0x120 drivers/usb/gadget/function/f_tcm.c:1825
 target_tpg_enable+0x2e5/0x590 drivers/target/target_core_tpg.c:481
 target_fabric_tpg_base_enable_store+0x122/0x1c0 drivers/target/target_core_fabric_configfs.c:840
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x33a/0x430 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61e/0xbb0 fs/read_write.c:687
 ksys_write+0x156/0x270 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: 0033:0x7fc7406be0d9
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:00007fc73e8f5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc740946090 RCX: 00007fc7406be0d9
RDX: 0000000000000002 RSI: 00002000000006c0 RDI: 0000000000000003
RBP: 00007fc740755024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc740946128 R14: 00007fc740946090 R15: 00007ffe5c21fcc8
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/17 07:31 upstream dcb68831eac7 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in tcm_register_callback
2026/08/04 15:24 upstream 848acc8ffe1b d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in tcm_register_callback
2026/08/17 09:48 linux-next 4477a78374a5 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root possible deadlock in tcm_register_callback
2026/08/19 19:17 git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git for-next 8da45c93dfa9 1e72964b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-riscv64 possible deadlock in tcm_register_callback
* Struck through repros no longer work on HEAD.