From: syzbot <syzbot+300213c2b5b55c0244f4@syzkaller.appspotmail.com>
To: a.hindborg@kernel.org, leitao@debian.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [fs?] possible deadlock in uvcg_extension_bm_controls_store
Date: Fri, 16 Oct 2026 00:34:26 -0700 [thread overview]
Message-ID: <6ad1d382.7952420f.283480.021e.GAE@google.com> (raw)
In-Reply-To: <6a83a769.4d75e56a.c9a88.0007.GAE@google.com>
syzbot has found a reproducer for the following issue on:
HEAD commit: 2f2f7eeef8b0 Merge tag 'soc-fixes-7.3-3' of git://git.kern..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=17d6dfd1580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c4b098695335c89f
dashboard link: https://syzkaller.appspot.com/bug?extid=300213c2b5b55c0244f4
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1394be8e580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+300213c2b5b55c0244f4@syzkaller.appspotmail.com
======================================================
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>
---
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:[~2026-10-16 7:34 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-18 0:29 [syzbot] [fs?] possible deadlock in uvcg_extension_bm_controls_store syzbot
2026-10-16 7:34 ` syzbot [this message]
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