possible deadlock in uvcg_default_processing_bm_controls_show

Status: upstream: reported C repro on 2026/10/20 07:07
Subsystems: fs
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+d123c96491067a2ee754@syzkaller.appspotmail.com
First crash: 4d04h, last: 1d06h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
f8e4d057 repro-c Reproduced: ✅ ❓ possible deadlock in uvcg_default_processing_bm_controls_show 2026/10/19 02:11 2026/10/19 02:11 2026/10/19 04:38 432c0077
eec7c7dc assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in uvcg_default_processing_bm_controls_show 2026/10/18 00:02 2026/10/18 00:02 2026/10/18 00:52 432c0077
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [fs?] possible deadlock in uvcg_default_processing_bm_controls_show 0 (1) 2026/10/20 07:07
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/10/19 04:39 13m retest repro git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a0ff06b3a7bd3aa0cd99d0294e60b3ed28c9bfac report job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor434/6013 is trying to acquire lock:
ffffffff91402ce8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408

but task is already holding lock:
ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&p->frag_sem){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5942 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
       down_write_killable+0x93/0x240 kernel/locking/rwsem.c:1643
       configfs_rmdir+0x3fa/0x950 fs/configfs/dir.c:1543
       vfs_rmdir fs/namei.c:5514 [inline]
       vfs_rmdir+0x328/0x8a0 fs/namei.c:5487
       filename_rmdir+0x31a/0x5c0 fs/namei.c:5571
       __do_sys_rmdir fs/namei.c:5594 [inline]
       __se_sys_rmdir fs/namei.c:5591 [inline]
       __ia32_sys_rmdir+0x45/0x60 fs/namei.c:5591
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #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:5409
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
       __do_sys_mkdir fs/namei.c:5469 [inline]
       __se_sys_mkdir fs/namei.c:5466 [inline]
       __ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #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+0x1a4/0x1bd0 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:5409
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
       __do_sys_mkdir fs/namei.c:5469 [inline]
       __se_sys_mkdir fs/namei.c:5466 [inline]
       __ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #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+0x1a4/0x1bd0 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:5409
       filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
       __do_sys_mkdir fs/namei.c:5469 [inline]
       __se_sys_mkdir fs/namei.c:5466 [inline]
       __ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #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+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       uvcg_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408
       fill_read_buffer fs/configfs/file.c:68 [inline]
       configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
       new_sync_read fs/read_write.c:493 [inline]
       vfs_read+0x82e/0xb40 fs/read_write.c:574
       ksys_read+0x12a/0x250 fs/read_write.c:716
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

locks held by syz-executor434/6013: 2, last CPU#1:
 #0: ffff8880500c0280 (&buffer->mutex){+.+.}-{4:4}, at: configfs_read_iter+0x79/0x6f0 fs/configfs/file.c:86
 #1: ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
 #1: ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 6013 Comm: syz-executor434 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+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 uvcg_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408
 fill_read_buffer fs/configfs/file.c:68 [inline]
 configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x82e/0xb40 fs/read_write.c:574
 ksys_read+0x12a/0x250 fs/read_write.c:716
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
 __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7ee5fec
Code: Unable to access opcode bytes at 0xf7ee5fc2.
RSP: 002b:00000000ff9e98b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000ff9e9970
RDX: 00000000000000ff RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/19 04:52 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a0ff06b3a7bd 432c0077 .config console log report C ci-qemu-upstream-386 possible deadlock in uvcg_default_processing_bm_controls_show
2026/10/19 02:09 upstream f909e534f5e3 432c0077 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in uvcg_default_processing_bm_controls_show
2026/10/17 14:19 upstream 58161ead29e5 432c0077 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvcg_default_processing_bm_controls_show
2026/10/17 14:18 upstream 58161ead29e5 432c0077 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvcg_default_processing_bm_controls_show
2026/10/16 06:58 upstream 2f2f7eeef8b0 3f2522c6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvcg_default_processing_bm_controls_show
2026/10/16 06:58 upstream 2f2f7eeef8b0 3f2522c6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvcg_default_processing_bm_controls_show
* Struck through repros no longer work on HEAD.