syzbot
possible deadlock in uvcg_extension_ba_source_id_store
Status:
upstream: reported on 2026/09/01 14:43
Subsystems:
fs
Labels:
prio:low
[Documentation on labels]
Reported-by: syzbot+76d92b6236b6ff1fc991@syzkaller.appspotmail.com
First crash: 50d, last: 3d01h
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Last patch testing requests (1)
Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G S L
------------------------------------------------------
syz.6.2036/13765 is trying to acquire lock:
ffffffff913ff8c8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_extension_ba_source_id_store+0xdb/0x430 drivers/usb/gadget/function/uvc_configfs.c:1046
but task is already holding lock:
ffff888034ee2b70 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
ffff888034ee2b70 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x218/0x4e0 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}:
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:5544 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5517
filename_rmdir+0x31a/0x5c0 fs/namei.c:5601
__do_sys_unlinkat fs/namei.c:5776 [inline]
__se_sys_unlinkat fs/namei.c:5769 [inline]
__x64_sys_unlinkat+0xf5/0x130 fs/namei.c:5769
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #3 (&sb->s_type->i_mutex_key#39){++++}-{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:5439
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5472
__do_sys_mkdirat fs/namei.c:5493 [inline]
__se_sys_mkdirat fs/namei.c:5490 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5490
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #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:5439
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5472
__do_sys_mkdirat fs/namei.c:5493 [inline]
__se_sys_mkdirat fs/namei.c:5490 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5490
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #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:5439
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5472
__do_sys_mkdirat fs/namei.c:5493 [inline]
__se_sys_mkdirat fs/namei.c:5490 [inline]
__x64_sys_mkdirat+0x89/0xc0 fs/namei.c:5490
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #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_extension_ba_source_id_store+0xdb/0x430 drivers/usb/gadget/function/uvc_configfs.c:1046
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 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#39 --> &p->frag_sem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(&p->frag_sem);
lock(&sb->s_type->i_mutex_key#39);
lock(&p->frag_sem);
lock(gadget_subsys.su_mutex);
*** DEADLOCK ***
locks held by syz.6.2036/13765: 4, last CPU#0:
#0: ffff88802f36f0b0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259
#1: ffff888020346460 (sb_writers#22){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#2: ffff88803636be80 (&buffer->mutex){+.+.}-{4:4}, at: configfs_write_iter+0x76/0x4e0 fs/configfs/file.c:226
#3: ffff888034ee2b70 (&p->frag_sem){++++}-{4:4}, at: flush_write_buffer fs/configfs/file.c:205 [inline]
#3: ffff888034ee2b70 (&p->frag_sem){++++}-{4:4}, at: configfs_write_iter+0x218/0x4e0 fs/configfs/file.c:229
stack backtrace:
CPU: 0 UID: 0 PID: 13765 Comm: syz.6.2036 Tainted: G S L syzkaller #0 PREEMPT(full)
Tainted: [S]=CPU_OUT_OF_SPEC, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
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_extension_ba_source_id_store+0xdb/0x430 drivers/usb/gadget/function/uvc_configfs.c:1046
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x302/0x4e0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6af/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2d1839e2d9
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:00007f2d1919e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f2d18625fa0 RCX: 00007f2d1839e2d9
RDX: 0000000000000011 RSI: 0000200000000440 RDI: 0000000000000007
RBP: 00007f2d18435888 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2d18626038 R14: 00007f2d18625fa0 R15: 00007fffa2d69018
</TASK>
Struck through repros no longer work on HEAD.