possible deadlock in configfs_rmdir

Status: upstream: reported on 2026/07/25 16:49
Reported-by: syzbot+22a2e230e9367df26d4a@syzkaller.appspotmail.com
First crash: 4d00h, last: 5h47m
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in configfs_rmdir 4 20 4h32m 4d08h 0/3 upstream: reported on 2026/07/25 09:00
linux-5.15 possible deadlock in configfs_rmdir 4 syz, C 16 7h30m 4d18h 0/3 upstream: reported C repro on 2026/07/24 22:09
upstream possible deadlock in configfs_rmdir prio:low fs 4 syz, C 500 now 1d03h 0/29 upstream: reported C repro on 2026/07/28 13:31

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.5217/23842 is trying to acquire lock:
ffffffff8db2b450 (&subsys->su_mutex){+.+.}-{3:3}, at: configfs_rmdir+0x63c/0x980 fs/configfs/dir.c:1556

but task is already holding lock:
ffff88805e660b80 (&sb->s_type->i_mutex_key#27){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
ffff88805e660b80 (&sb->s_type->i_mutex_key#27){++++}-{3:3}, at: vfs_rmdir+0xee/0x4b0 fs/namei.c:4197

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&sb->s_type->i_mutex_key#27){++++}-{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:4125
       do_mkdirat+0x1dc/0x450 fs/namei.c:4148
       __do_sys_mkdir fs/namei.c:4168 [inline]
       __se_sys_mkdir fs/namei.c:4166 [inline]
       __x64_sys_mkdir+0x6e/0x80 fs/namei.c:4166
       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 (&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:4125
       do_mkdirat+0x1dc/0x450 fs/namei.c:4148
       __do_sys_mkdir fs/namei.c:4168 [inline]
       __se_sys_mkdir fs/namei.c:4166 [inline]
       __x64_sys_mkdir+0x6e/0x80 fs/namei.c:4166
       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 (tpg_instances_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x135/0xc80 kernel/locking/mutex.c:747
       usbg_make_tpg+0xf8/0x580 drivers/usb/gadget/function/f_tcm.c:1324
       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:4125
       do_mkdirat+0x1dc/0x450 fs/namei.c:4148
       __do_sys_mkdir fs/namei.c:4168 [inline]
       __se_sys_mkdir fs/namei.c:4166 [inline]
       __x64_sys_mkdir+0x6e/0x80 fs/namei.c:4166
       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 (&subsys->su_mutex){+.+.}-{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
       configfs_rmdir+0x63c/0x980 fs/configfs/dir.c:1556
       vfs_rmdir+0x352/0x4b0 fs/namei.c:4208
       do_rmdir+0x29f/0x590 fs/namei.c:4267
       __do_sys_rmdir fs/namei.c:4286 [inline]
       __se_sys_rmdir fs/namei.c:4284 [inline]
       __x64_sys_rmdir+0x49/0x50 fs/namei.c:4284
       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:
  &subsys->su_mutex --> &opts->dep_lock --> &sb->s_type->i_mutex_key#27

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#27);
                               lock(&opts->dep_lock);
                               lock(&sb->s_type->i_mutex_key#27);
  lock(&subsys->su_mutex);

 *** DEADLOCK ***

3 locks held by syz.3.5217/23842:
 #0: ffff888018f22418 (sb_writers#22){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:412
 #1: ffff88805e660670 (&sb->s_type->i_mutex_key#7/1){+.+.}-{3:3}, at: inode_lock_nested include/linux/fs.h:839 [inline]
 #1: ffff88805e660670 (&sb->s_type->i_mutex_key#7/1){+.+.}-{3:3}, at: do_rmdir+0x1c6/0x590 fs/namei.c:4255
 #2: ffff88805e660b80 (&sb->s_type->i_mutex_key#27){++++}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
 #2: ffff88805e660b80 (&sb->s_type->i_mutex_key#27){++++}-{3:3}, at: vfs_rmdir+0xee/0x4b0 fs/namei.c:4197

stack backtrace:
CPU: 0 PID: 23842 Comm: syz.3.5217 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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
 configfs_rmdir+0x63c/0x980 fs/configfs/dir.c:1556
 vfs_rmdir+0x352/0x4b0 fs/namei.c:4208
 do_rmdir+0x29f/0x590 fs/namei.c:4267
 __do_sys_rmdir fs/namei.c:4286 [inline]
 __se_sys_rmdir fs/namei.c:4284 [inline]
 __x64_sys_rmdir+0x49/0x50 fs/namei.c:4284
 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: 0033:0x7fd4ae39de99
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:00007fd4af32c028 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00007fd4ae626090 RCX: 00007fd4ae39de99
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000280
RBP: 00007fd4ae433eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd4ae626128 R14: 00007fd4ae626090 R15: 00007ffc861466b8
 </TASK>

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/29 11:20 linux-6.6.y c5596480c50e 19622d9d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/29 11:20 linux-6.6.y c5596480c50e 19622d9d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/29 11:14 linux-6.6.y c5596480c50e 19622d9d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/29 11:14 linux-6.6.y c5596480c50e 19622d9d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/27 22:09 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/27 22:09 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/26 05:05 linux-6.6.y c5596480c50e 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
2026/07/25 16:48 linux-6.6.y c5596480c50e 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan possible deadlock in configfs_rmdir
* Struck through repros no longer work on HEAD.