possible deadlock in tcm_alloc

Status: upstream: reported on 2026/08/04 20:57
Reported-by: syzbot+ea06458b17a727d0decd@syzkaller.appspotmail.com
First crash: 1d08h, last: 1d02h
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in tcm_alloc prio:low usb 4 syz, C 145 12h45m 2d18h 0/29 upstream: reported C repro on 2026/08/03 10:48
linux-6.1 possible deadlock in tcm_alloc 4 24 1d03h 1d08h 0/3 upstream: reported on 2026/08/04 21:00
linux-5.15 possible deadlock in tcm_alloc 4 14 1d03h 1d10h 0/3 upstream: reported on 2026/08/04 18:59

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.2/5836 is trying to acquire lock:
ffffffff8de58f08 (tpg_instances_lock){+.+.}-{3:3}, at: tcm_alloc+0x21/0x1e0 drivers/usb/gadget/function/f_tcm.c:2247

but task is already holding lock:
ffff888020fc4398 (&gi->lock){+.+.}-{3:3}, at: config_usb_cfg_link+0x59/0x250 drivers/usb/gadget/configfs.c:439

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&gi->lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       config_usb_cfg_link+0x59/0x250 drivers/usb/gadget/configfs.c:439
       configfs_symlink+0x5a5/0xfe0 fs/configfs/symlink.c:202
       vfs_symlink+0x138/0x2b0 fs/namei.c:4528
       do_symlinkat+0x1ba/0x400 fs/namei.c:4554
       __do_sys_symlinkat fs/namei.c:4570 [inline]
       __se_sys_symlinkat fs/namei.c:4567 [inline]
       __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4567
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #2 (&sb->s_type->i_mutex_key#20){++++}-{3:3}:
       down_write+0x97/0x200 kernel/locking/rwsem.c:1573
       inode_lock include/linux/fs.h:804 [inline]
       configfs_depend_item_unlocked+0x157/0x430 fs/configfs/dir.c:1255
       usbg_make_tpg+0x1f7/0x580 drivers/usb/gadget/function/f_tcm.c:1341
       target_fabric_make_tpg+0xa4/0x6d0 drivers/target/target_core_fabric_configfs.c:939
       configfs_mkdir+0x515/0x9e0 fs/configfs/dir.c:1360
       vfs_mkdir+0x2a5/0x470 fs/namei.c:4168
       do_mkdirat+0x1dc/0x450 fs/namei.c:4191
       __do_sys_mkdirat fs/namei.c:4206 [inline]
       __se_sys_mkdirat fs/namei.c:4204 [inline]
       __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4204
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&opts->dep_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       usbg_make_tpg+0x148/0x580 drivers/usb/gadget/function/f_tcm.c:1333
       target_fabric_make_tpg+0xa4/0x6d0 drivers/target/target_core_fabric_configfs.c:939
       configfs_mkdir+0x515/0x9e0 fs/configfs/dir.c:1360
       vfs_mkdir+0x2a5/0x470 fs/namei.c:4168
       do_mkdirat+0x1dc/0x450 fs/namei.c:4191
       __do_sys_mkdirat fs/namei.c:4206 [inline]
       __se_sys_mkdirat fs/namei.c:4204 [inline]
       __x64_sys_mkdirat+0x89/0xa0 fs/namei.c:4204
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (tpg_instances_lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
       lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       tcm_alloc+0x21/0x1e0 drivers/usb/gadget/function/f_tcm.c:2247
       usb_get_function+0x5d/0xb0 drivers/usb/gadget/functions.c:61
       config_usb_cfg_link+0x148/0x250 drivers/usb/gadget/configfs.c:469
       configfs_symlink+0x5a5/0xfe0 fs/configfs/symlink.c:202
       vfs_symlink+0x138/0x2b0 fs/namei.c:4528
       do_symlinkat+0x1ba/0x400 fs/namei.c:4554
       __do_sys_symlinkat fs/namei.c:4570 [inline]
       __se_sys_symlinkat fs/namei.c:4567 [inline]
       __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4567
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
  tpg_instances_lock --> &sb->s_type->i_mutex_key#20 --> &gi->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&gi->lock);
                               lock(&sb->s_type->i_mutex_key#20);
                               lock(&gi->lock);
  lock(tpg_instances_lock);

 *** DEADLOCK ***

3 locks held by syz.1.2/5836:
 #0: ffff88801faae418 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:412
 #1: ffff88805d60c160 (&sb->s_type->i_mutex_key#20){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
 #1: ffff88805d60c160 (&sb->s_type->i_mutex_key#20){++++}-{3:3}, at: configfs_symlink+0x47a/0xfe0 fs/configfs/symlink.c:192
 #2: ffff888020fc4398 (&gi->lock){+.+.}-{3:3}, at: config_usb_cfg_link+0x59/0x250 drivers/usb/gadget/configfs.c:439

stack backtrace:
CPU: 1 PID: 5836 Comm: syz.1.2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x37ef/0x7d80 kernel/locking/lockdep.c:5137
 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
 tcm_alloc+0x21/0x1e0 drivers/usb/gadget/function/f_tcm.c:2247
 usb_get_function+0x5d/0xb0 drivers/usb/gadget/functions.c:61
 config_usb_cfg_link+0x148/0x250 drivers/usb/gadget/configfs.c:469
 configfs_symlink+0x5a5/0xfe0 fs/configfs/symlink.c:202
 vfs_symlink+0x138/0x2b0 fs/namei.c:4528
 do_symlinkat+0x1ba/0x400 fs/namei.c:4554
 __do_sys_symlinkat fs/namei.c:4570 [inline]
 __se_sys_symlinkat fs/namei.c:4567 [inline]
 __x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4567
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f545ed9e019
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:00007f545cff6028 EFLAGS: 00000246 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 00007f545f025fa0 RCX: 00007f545ed9e019
RDX: 0000200000000880 RSI: ffffffffffffff9c RDI: 0000200000000840
RBP: 00007f545ee3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f545f026038 R14: 00007f545f025fa0 R15: 00007ffe2f0c6788
 </TASK>

Crashes (14):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/05 02:23 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/05 01:10 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/05 01:10 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/05 00:41 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/05 00:37 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/05 00:18 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 23:34 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 23:33 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 22:24 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 22:24 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 22:23 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 21:56 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 21:56 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
2026/08/04 20:56 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in tcm_alloc
* Struck through repros no longer work on HEAD.