From: syzbot <syzbot+8c0a48f6c8357c9da819@syzkaller.appspotmail.com>
To: gregkh@linuxfoundation.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [usb?] [fs?] possible deadlock in uvc_func_allow_link
Date: Tue, 20 Oct 2026 02:32:33 -0700 [thread overview]
Message-ID: <6ad73531.5c73e770.1a06c9.0104.GAE@google.com> (raw)
In-Reply-To: <6a6944b4.d9e86bb5.297b12.003c.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: f47d223627f8 Merge tag 'vfs-7.4-rc1.sync_close' of git://g..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1475c831580000
kernel config: https://syzkaller.appspot.com/x/.config?x=897740d587b37862
dashboard link: https://syzkaller.appspot.com/bug?extid=8c0a48f6c8357c9da819
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1275c831580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8c0a48f6c8357c9da819@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor238/6025 is trying to acquire lock:
ffffffff914019a8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
but task is already holding lock:
ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: configfs_symlink+0x452/0x1340 fs/configfs/symlink.c:201
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #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:5420
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
__do_sys_mkdir fs/namei.c:5480 [inline]
__se_sys_mkdir fs/namei.c:5477 [inline]
__x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
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+0x1a4/0x1c20 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:5420
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
__do_sys_mkdir fs/namei.c:5480 [inline]
__se_sys_mkdir fs/namei.c:5477 [inline]
__x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
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+0x1a4/0x1c20 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:5420
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5453
__do_sys_mkdir fs/namei.c:5480 [inline]
__se_sys_mkdir fs/namei.c:5477 [inline]
__x64_sys_mkdir+0x6b/0x90 fs/namei.c:5477
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+0x1a4/0x1c20 kernel/locking/mutex.c:821
uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
configfs_symlink+0x695/0x1340 fs/configfs/symlink.c:211
vfs_symlink fs/namei.c:5804 [inline]
vfs_symlink+0x178/0x4d0 fs/namei.c:5783
filename_symlinkat+0x2a6/0x560 fs/namei.c:5829
__do_sys_symlink fs/namei.c:5856 [inline]
__se_sys_symlink fs/namei.c:5852 [inline]
__x64_sys_symlink+0x79/0xb0 fs/namei.c:5852
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 --> tpg_instances_lock --> &sb->s_type->i_mutex_key#25
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&sb->s_type->i_mutex_key#25);
lock(tpg_instances_lock);
lock(&sb->s_type->i_mutex_key#25);
lock(gadget_subsys.su_mutex);
*** DEADLOCK ***
locks held by syz-executor238/6025: 2, last CPU#3:
#0: ffff888025b44460 (sb_writers#13){.+.+}-{0:0}, at: filename_create+0x10d/0x400 fs/namei.c:5095
#1: ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
#1: ffff88802eca5b80 (&sb->s_type->i_mutex_key#25){+.+.}-{4:4}, at: configfs_symlink+0x452/0x1340 fs/configfs/symlink.c:201
stack backtrace:
CPU: 3 UID: 0 PID: 6025 Comm: syz-executor238 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+0x1a4/0x1c20 kernel/locking/mutex.c:821
uvc_func_allow_link+0x76/0x3f0 drivers/usb/gadget/function/uvc_configfs.c:3651
configfs_symlink+0x695/0x1340 fs/configfs/symlink.c:211
vfs_symlink fs/namei.c:5804 [inline]
vfs_symlink+0x178/0x4d0 fs/namei.c:5783
filename_symlinkat+0x2a6/0x560 fs/namei.c:5829
__do_sys_symlink fs/namei.c:5856 [inline]
__se_sys_symlink fs/namei.c:5852 [inline]
__x64_sys_symlink+0x79/0xb0 fs/namei.c:5852
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: 0033:0x7f17e04c5357
Code: 77 01 c3 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 b8 58 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 d8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffdfd785e48 EFLAGS: 00000206 ORIG_RAX: 0000000000000058
RAX: ffffffffffffffda RBX: 00007f17e051e1e8 RCX: 00007f17e04c5357
RDX: 0000000000000000 RSI: 00007f17e051e170 RDI: 00007f17e051e1e8
RBP: 00007f17e051e300 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 00007f17e051e250
R13: 00007f17e051e298 R14: 00007f17e051e2d8 R15: 00007f17e051e1b0
</TASK>
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
prev parent reply other threads:[~2026-10-20 9:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-29 0:09 [syzbot] [usb?] " syzbot
2026-10-20 9:32 ` syzbot [this message]
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