* [syzbot] [fs?] possible deadlock in uvcg_format_bma_controls_store
@ 2026-09-16 2:15 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-09-16 2:15 UTC (permalink / raw)
To: a.hindborg, leitao, linux-fsdevel, linux-kernel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: 3026c6e4f223 Merge tag 'slab-for-7.3-rc2' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11f1e901580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
dashboard link: https://syzkaller.appspot.com/bug?extid=50560f9ba016e97e2023
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/98fa15ee8f48/disk-3026c6e4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/36b1db5cf167/vmlinux-3026c6e4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3f745756a36c/bzImage-3026c6e4.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+50560f9ba016e97e2023@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.3.8436/729 is trying to acquire lock:
ffffffff8fc11b68 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_format_bma_controls_store+0x55/0x2b0 drivers/usb/gadget/function/uvc_configfs.c:1707
but task is already holding lock:
ffff888028d20770 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff888028d20770 (&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:5515
filename_rmdir+0x292/0x520 fs/namei.c:5572
__do_sys_unlinkat fs/namei.c:5747 [inline]
__se_sys_unlinkat+0x71/0x1a0 fs/namei.c:5740
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#27){++++}-{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:5410
filename_mkdirat+0x285/0x510 fs/namei.c:5443
__do_sys_mkdir fs/namei.c:5470 [inline]
__se_sys_mkdir+0x34/0x150 fs/namei.c:5467
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:5410
filename_mkdirat+0x285/0x510 fs/namei.c:5443
__do_sys_mkdir fs/namei.c:5470 [inline]
__se_sys_mkdir+0x34/0x150 fs/namei.c:5467
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:5410
filename_mkdirat+0x285/0x510 fs/namei.c:5443
__do_sys_mkdir fs/namei.c:5470 [inline]
__se_sys_mkdir+0x34/0x150 fs/namei.c:5467
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_format_bma_controls_store+0x55/0x2b0 drivers/usb/gadget/function/uvc_configfs.c:1707
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#27 --> &p->frag_sem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(&p->frag_sem);
lock(&sb->s_type->i_mutex_key#27);
lock(&p->frag_sem);
lock(gadget_subsys.su_mutex);
*** DEADLOCK ***
locks held by syz.3.8436/729: 4, last CPU#1:
#0: ffff88802cacd270 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259
#1: ffff88801d716460 (sb_writers#16){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline]
#1: ffff88801d716460 (sb_writers#16){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
#2: ffff888076ff2c80 (&buffer->mutex#2){+.+.}-{4:4}, at: configfs_write_iter+0x7e/0x430 fs/configfs/file.c:226
#3: ffff888028d20770 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
#3: ffff888028d20770 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x238/0x430 fs/configfs/file.c:229
stack backtrace:
CPU: 1 UID: 0 PID: 729 Comm: syz.3.8436 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
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_format_bma_controls_store+0x55/0x2b0 drivers/usb/gadget/function/uvc_configfs.c:1707
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: 0033:0x7fee74b9e159
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:00007fee7597e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fee74e25fa0 RCX: 00007fee74b9e159
RDX: 0000000000000002 RSI: 0000200000000300 RDI: 0000000000000003
RBP: 00007fee74c3503b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fee74e26038 R14: 00007fee74e25fa0 R15: 00007ffd3a9e87e8
</TASK>
---
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