* [syzbot] [fs?] possible deadlock in uvcg_default_processing_bm_controls_show
@ 2026-10-20 7:07 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-10-20 7:07 UTC (permalink / raw)
To: linux-fsdevel, linux-kernel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: a0ff06b3a7bd Merge tag 'firewire-fixes-7.3-final' of git:/..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=10c64bc9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=44ac479246d4559b
dashboard link: https://syzkaller.appspot.com/bug?extid=d123c96491067a2ee754
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11cb5495580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d123c96491067a2ee754@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor434/6013 is trying to acquire lock:
ffffffff91402ce8 (gadget_subsys.su_mutex){+.+.}-{4:4}, at: uvcg_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408
but task is already holding lock:
ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88
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:5514 [inline]
vfs_rmdir+0x328/0x8a0 fs/namei.c:5487
filename_rmdir+0x31a/0x5c0 fs/namei.c:5571
__do_sys_rmdir fs/namei.c:5594 [inline]
__se_sys_rmdir fs/namei.c:5591 [inline]
__ia32_sys_rmdir+0x45/0x60 fs/namei.c:5591
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
-> #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:5409
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
__do_sys_mkdir fs/namei.c:5469 [inline]
__se_sys_mkdir fs/namei.c:5466 [inline]
__ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
-> #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:5409
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
__do_sys_mkdir fs/namei.c:5469 [inline]
__se_sys_mkdir fs/namei.c:5466 [inline]
__ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
-> #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:5409
filename_mkdirat+0x48b/0x5e0 fs/namei.c:5442
__do_sys_mkdir fs/namei.c:5469 [inline]
__se_sys_mkdir fs/namei.c:5466 [inline]
__ia32_sys_mkdir+0x6a/0x90 fs/namei.c:5466
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
-> #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_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408
fill_read_buffer fs/configfs/file.c:68 [inline]
configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x82e/0xb40 fs/read_write.c:574
ksys_read+0x12a/0x250 fs/read_write.c:716
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
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-executor434/6013: 2, last CPU#1:
#0: ffff8880500c0280 (&buffer->mutex){+.+.}-{4:4}, at: configfs_read_iter+0x79/0x6f0 fs/configfs/file.c:86
#1: ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: fill_read_buffer fs/configfs/file.c:66 [inline]
#1: ffff888000c93470 (&p->frag_sem){++++}-{4:4}, at: configfs_read_iter+0x346/0x6f0 fs/configfs/file.c:88
stack backtrace:
CPU: 1 UID: 0 PID: 6013 Comm: syz-executor434 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+0x1a4/0x1bd0 kernel/locking/mutex.c:821
uvcg_default_processing_bm_controls_show+0x57/0x2a0 drivers/usb/gadget/function/uvc_configfs.c:408
fill_read_buffer fs/configfs/file.c:68 [inline]
configfs_read_iter+0x426/0x6f0 fs/configfs/file.c:88
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x82e/0xb40 fs/read_write.c:574
ksys_read+0x12a/0x250 fs/read_write.c:716
do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
__do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7ee5fec
Code: Unable to access opcode bytes at 0xf7ee5fc2.
RSP: 002b:00000000ff9e98b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000ff9e9970
RDX: 00000000000000ff RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
---
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