possible deadlock in uvcg_extension_bm_controls_store

Status: upstream: reported C repro on 2026/08/18 00:29
Subsystems: fs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+300213c2b5b55c0244f4@syzkaller.appspotmail.com
First crash: 63d, last: 4h40m
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
d26c4a6c repro-c Reproduced: ✅ ❓ possible deadlock in uvcg_extension_bm_controls_store 2026/10/16 00:01 2026/10/16 00:01 2026/10/16 02:28 3f2522c6
296bca29 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in uvcg_extension_bm_controls_store 2026/08/16 00:01 2026/08/16 00:01 2026/08/16 01:06 746171ee
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [fs?] possible deadlock in uvcg_extension_bm_controls_store 0 (2) 2026/10/16 07:34
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/10/16 07:12 20m retest repro git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e report job log log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor184/5998 is trying to acquire lock:
ffffffff90c14b28 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125

but task is already holding lock:
ffff888028accd70 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff888028accd70 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x238/0x430 fs/configfs/file.c:229

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&p->frag_sem){++++}-{4:4}:
       down_write_killable+0xa6/0x240 kernel/locking/rwsem.c:1643
       configfs_rmdir+0x3b0/0x950 fs/configfs/dir.c:1543
       vfs_rmdir+0x3e6/0x6a0 fs/namei.c:5544
       filename_rmdir+0x292/0x520 fs/namei.c:5601
       __do_sys_rmdir fs/namei.c:5624 [inline]
       __se_sys_rmdir+0x2e/0x140 fs/namei.c:5621
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&sb->s_type->i_mutex_key#25){++++}-{4:4}:
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       inode_lock include/linux/fs.h:1024 [inline]
       configfs_depend_item_unlocked+0x153/0x420 fs/configfs/dir.c:1268
       usbg_make_tpg+0x1e0/0x550 drivers/usb/gadget/function/f_tcm.c:1692
       target_fabric_make_tpg+0xa8/0x6d0 drivers/target/target_core_fabric_configfs.c:947
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x40c/0x620 fs/namei.c:5439
       filename_mkdirat+0x285/0x510 fs/namei.c:5472
       __do_sys_mkdir fs/namei.c:5499 [inline]
       __se_sys_mkdir+0x34/0x150 fs/namei.c:5496
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (tpg_instances_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       tcm_alloc_inst+0x65/0x1a0 drivers/usb/gadget/function/f_tcm.c:2687
       try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
       usb_get_function_instance+0xe3/0x2f0 drivers/usb/gadget/functions.c:44
       function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x40c/0x620 fs/namei.c:5439
       filename_mkdirat+0x285/0x510 fs/namei.c:5472
       __do_sys_mkdir fs/namei.c:5499 [inline]
       __se_sys_mkdir+0x34/0x150 fs/namei.c:5496
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (func_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       try_get_usb_function_instance drivers/usb/gadget/functions.c:18 [inline]
       usb_get_function_instance+0x2e/0x2f0 drivers/usb/gadget/functions.c:44
       function_make+0x127/0x360 drivers/usb/gadget/configfs.c:626
       configfs_mkdir+0x4f6/0x9e0 fs/configfs/dir.c:1369
       vfs_mkdir+0x40c/0x620 fs/namei.c:5439
       filename_mkdirat+0x285/0x510 fs/namei.c:5472
       __do_sys_mkdir fs/namei.c:5499 [inline]
       __se_sys_mkdir+0x34/0x150 fs/namei.c:5496
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (gadget_subsys.su_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125
       flush_write_buffer fs/configfs/file.c:207 [inline]
       configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

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-executor184/5998: 3, last CPU#1:
 #0: ffff88801e7d8460 (sb_writers#12){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2756 [inline]
 #0: ffff88801e7d8460 (sb_writers#12){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
 #1: ffff888070770c80 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x7e/0x430 fs/configfs/file.c:226
 #2: ffff888028accd70 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
 #2: ffff888028accd70 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x238/0x430 fs/configfs/file.c:229

stack backtrace:
CPU: 1 UID: 0 PID: 5998 Comm: syz-executor184 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 uvcg_extension_bm_controls_store+0xe4/0xb00 drivers/usb/gadget/function/uvc_configfs.c:1125
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa3e20116b7
Code: 48 89 fa 4c 89 df e8 98 1d 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffcaf360150 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000055558f99e400 RCX: 00007fa3e20116b7
RDX: 0000000000000002 RSI: 00007fa3e204d174 RDI: 0000000000000003
RBP: 00007fa3e204fc38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007ffcaf360230
R13: 000055558f99fdb0 R14: 000055558f99e3d8 R15: 000055558f9a7e4b
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/16 07:33 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 2f2f7eeef8b0 a9ede23c .config console log report C ci-upstream-kasan-gce-root possible deadlock in uvcg_extension_bm_controls_store
2026/08/14 00:23 upstream 3aa1dcaa4f6f a9ede23c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in uvcg_extension_bm_controls_store
2026/10/15 11:23 upstream 0fcb05b72344 8fb0ae89 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in uvcg_extension_bm_controls_store
* Struck through repros no longer work on HEAD.