possible deadlock in configfs_detach_group

Status: upstream: reported on 2026/08/11 00:24
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+245b08b227dcdeb63e2c@syzkaller.appspotmail.com
First crash: 5d18h, last: 5d18h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
afdc787d assessment-security 💥 possible deadlock in configfs_detach_group 2026/08/11 00:57 2026/08/11 00:57 2026/08/11 00:57 039457bd
63794911 assessment-security 💥 possible deadlock in configfs_detach_group 2026/08/09 02:29 2026/08/09 02:29 2026/08/09 02:29 5d63f80b
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Title Replies (including bot) Last reply
[syzbot] [fs?] possible deadlock in configfs_detach_group 0 (1) 2026/08/11 00:24

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.304/7178 is trying to acquire lock:
ffff8880005e4880 (&default_group_class[depth - 1]#9){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff8880005e4880 (&default_group_class[depth - 1]#9){+.+.}-{4:4}, at: detach_groups fs/configfs/dir.c:680 [inline]
ffff8880005e4880 (&default_group_class[depth - 1]#9){+.+.}-{4:4}, at: configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887

but task is already holding lock:
ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: detach_groups fs/configfs/dir.c:680 [inline]
ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&default_group_class[depth - 1]#8){++++}-{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]
       detach_groups fs/configfs/dir.c:680 [inline]
       configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887
       detach_groups fs/configfs/dir.c:682 [inline]
       configfs_detach_group+0x224/0x440 fs/configfs/dir.c:887
       configfs_rmdir+0x598/0x950 fs/configfs/dir.c:1554
       vfs_rmdir fs/namei.c:5381 [inline]
       vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
       filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
       __do_sys_rmdir fs/namei.c:5461 [inline]
       __se_sys_rmdir fs/namei.c:5458 [inline]
       __ia32_sys_rmdir+0x45/0x60 fs/namei.c:5458
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #4 (&default_group_class[depth - 1]#2){+.+.}-{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]
       detach_groups fs/configfs/dir.c:680 [inline]
       configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887
       configfs_rmdir+0x598/0x950 fs/configfs/dir.c:1554
       vfs_rmdir fs/namei.c:5381 [inline]
       vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
       filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
       __do_sys_rmdir fs/namei.c:5461 [inline]
       __se_sys_rmdir fs/namei.c:5458 [inline]
       __ia32_sys_rmdir+0x45/0x60 fs/namei.c:5458
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #3 (&sb->s_type->i_mutex_key#26){++++}-{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_mkdir fs/namei.c:5336 [inline]
       __se_sys_mkdir fs/namei.c:5333 [inline]
       __ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5333
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #2 (&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:2669
       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_mkdir fs/namei.c:5336 [inline]
       __se_sys_mkdir fs/namei.c:5333 [inline]
       __ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5333
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #1 (gadget_subsys.su_mutex){+.+.}-{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
       uvcg_streaming_class_allow_link+0x100/0x6b0 drivers/usb/gadget/function/uvc_configfs.c:3432
       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_symlinkat fs/namei.c:5705 [inline]
       __se_sys_symlinkat fs/namei.c:5700 [inline]
       __ia32_sys_symlinkat+0x9b/0xe0 fs/namei.c:5700
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #0 (&default_group_class[depth - 1]#9){+.+.}-{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
       down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
       inode_lock include/linux/fs.h:1024 [inline]
       detach_groups fs/configfs/dir.c:680 [inline]
       configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887
       detach_groups fs/configfs/dir.c:682 [inline]
       configfs_detach_group+0x224/0x440 fs/configfs/dir.c:887
       detach_groups fs/configfs/dir.c:682 [inline]
       configfs_detach_group+0x224/0x440 fs/configfs/dir.c:887
       configfs_rmdir+0x598/0x950 fs/configfs/dir.c:1554
       vfs_rmdir fs/namei.c:5381 [inline]
       vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
       filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
       __do_sys_rmdir fs/namei.c:5461 [inline]
       __se_sys_rmdir fs/namei.c:5458 [inline]
       __ia32_sys_rmdir+0x45/0x60 fs/namei.c:5458
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

other info that might help us debug this:

Chain exists of:
  &default_group_class[depth - 1]#9 --> &default_group_class[depth - 1]#2 --> &default_group_class[depth - 1]#8

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&default_group_class[depth - 1]#8);
                               lock(&default_group_class[depth - 1]#2);
                               lock(&default_group_class[depth - 1]#8);
  lock(&default_group_class[depth - 1]#9);

 *** DEADLOCK ***

5 locks held by syz.3.304/7178:
 #0: ffff88802250c450 (sb_writers#15){.+.+}-{0:0}, at: filename_rmdir+0x1ff/0x5c0 fs/namei.c:5427
 #1: ffff888013f76e80 (&default_group_class[depth - 1]#2/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1069 [inline]
 #1: ffff888013f76e80 (&default_group_class[depth - 1]#2/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2918 [inline]
 #1: ffff888013f76e80 (&default_group_class[depth - 1]#2/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2942 [inline]
 #1: ffff888013f76e80 (&default_group_class[depth - 1]#2/1){+.+.}-{4:4}, at: filename_rmdir+0x258/0x5c0 fs/namei.c:5431
 #2: ffff8880005e0f80 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #2: ffff8880005e0f80 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: vfs_rmdir fs/namei.c:5366 [inline]
 #2: ffff8880005e0f80 (&sb->s_type->i_mutex_key#26){++++}-{4:4}, at: vfs_rmdir+0xed/0x8a0 fs/namei.c:5354
 #3: ffff8880005e6e80 (&default_group_class[depth - 1]#2){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #3: ffff8880005e6e80 (&default_group_class[depth - 1]#2){+.+.}-{4:4}, at: detach_groups fs/configfs/dir.c:680 [inline]
 #3: ffff8880005e6e80 (&default_group_class[depth - 1]#2){+.+.}-{4:4}, at: configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887
 #4: ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #4: ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: detach_groups fs/configfs/dir.c:680 [inline]
 #4: ffff8880005e1900 (&default_group_class[depth - 1]#8){++++}-{4:4}, at: configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887

stack backtrace:
CPU: 3 UID: 0 PID: 7178 Comm: syz.3.304 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+0x178/0x1c7 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
 down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
 inode_lock include/linux/fs.h:1024 [inline]
 detach_groups fs/configfs/dir.c:680 [inline]
 configfs_detach_group+0x21c/0x440 fs/configfs/dir.c:887
 detach_groups fs/configfs/dir.c:682 [inline]
 configfs_detach_group+0x224/0x440 fs/configfs/dir.c:887
 detach_groups fs/configfs/dir.c:682 [inline]
 configfs_detach_group+0x224/0x440 fs/configfs/dir.c:887
 configfs_rmdir+0x598/0x950 fs/configfs/dir.c:1554
 vfs_rmdir fs/namei.c:5381 [inline]
 vfs_rmdir+0x328/0x8a0 fs/namei.c:5354
 filename_rmdir+0x31a/0x5c0 fs/namei.c:5438
 __do_sys_rmdir fs/namei.c:5461 [inline]
 __se_sys_rmdir fs/namei.c:5458 [inline]
 __ia32_sys_rmdir+0x45/0x60 fs/namei.c:5458
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7ff3fec
Code: Unable to access opcode bytes at 0xf7ff3fc2.
RSP: 002b:00000000f54b650c EFLAGS: 00000292 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000080000200 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/05 15:49 upstream c21bb4193868 1eed00d1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in configfs_detach_group
* Struck through repros no longer work on HEAD.