Re: [syzbot] [media?] WARNING in vidtv_stop_feed

[Jeffin Philip]

On Fri, Aug 28 2026, syzbot wrote:

>------------[ cut here ]------------
>DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>WARNING: kernel/locking/mutex.c:625 at __mutex_lock_common kernel/locking/mutex.c:625 [inline], CPU>3: syz.3.334/7114
>WARNING: kernel/locking/mutex.c:625 at __mutex_lock+0x944/0x1bc0 kernel/locking/mutex.c:821, CPU>3: syz.3.334/7114
>Modules linked in:
>CPU: 3 UID: 0 PID: 7114 Comm: syz.3.334 Tainted: G             L      syzkaller >0 PREEMPT(full) 
>Tainted: [L]=SOFTLOCKUP
>Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:625 [inline]
>RIP: 0010:__mutex_lock+0x94b/0x1bc0 kernel/locking/mutex.c:821
>Code: 0f b6 14 11 38 d0 7c 08 84 d2 0f 85 b4 10 00 00 44 8b 05 b8 11 7a 05 45 85 c0 75 13 48 8d 3d 9c 16 7d 05 48 c7 c6 80 d3 ef 8b <67> 48 0f b9 3a 90 e9 1b f8 ff ff 4d 8d a7 f0 0a 00 00 4c 89 e7 e8
>RSP: 0000:ffffc90025f2fae0 EFLAGS: 00010246
>RAX: 0000000000000003 RBX: ffff888029f2d128 RCX: 1ffffffff22898cc
>RDX: 0000000000000000 RSI: ffffffff8befd380 RDI: ffffffff9147cb50
>RBP: ffffc90025f2fc50 R08: 0000000000000000 R09: 0000000000000000
>R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>R13: 0000000000000000 R14: dffffc0000000000 R15: 0000000000000000
>FS:  0000000000000000(0000) GS:ffff888096c84000(0063) knlGS:0000000057892480
>CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
>CR2: 00000000f544aff4 CR3: 00000000577a8000 CR4: 0000000000352ef0
>Call Trace:
> <TASK>
> vidtv_stop_feed+0x75/0x2a0 drivers/media/test-drivers/vidtv/vidtv_bridge.c:256
> dmx_ts_feed_stop_filtering+0xe9/0x1d0 drivers/media/dvb-core/dvb_demux.c:780
> dvb_dmxdev_feed_stop.isra.0+0x162/0x270 drivers/media/dvb-core/dmxdev.c:494
> dvb_dmxdev_filter_stop+0x1d0/0x390 drivers/media/dvb-core/dmxdev.c:572
> dvb_dmxdev_filter_free drivers/media/dvb-core/dmxdev.c:856 [inline]
> dvb_demux_release+0x92/0x560 drivers/media/dvb-core/dmxdev.c:1256
> __fput+0x3ff/0xb50 fs/file_table.c:512
> task_work_run+0x150/0x240 kernel/task_work.c:233
> resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
> __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
> exit_to_user_mode_loop+0x1d8/0x700 kernel/entry/common.c:101
> __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
> syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
> syscall_exit_to_user_mode include/linux/entry-common.h:336 [inline]
> __do_fast_syscall_32+0x59f/0x8b0 arch/x86/entry/syscall_32.c:294
> do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
> entry_SYSENTER_compat_after_hwframe+0x84/0x8e
>RIP: 0023:0xf6ffefec
>Code: Unable to access opcode bytes at 0xf6ffefc2.
>RSP: 002b:00000000ffb45dfc EFLAGS: 00000202 ORIG_RAX: 00000000000001b4
>RAX: 0000000000000000 RBX: 0000000000000003 RCX: 000000000000001e
>RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
>R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> </TASK>
>----------------
>Code disassembly (best guess):
>   0:	0f b6 14 11          	movzbl (%rcx,%rdx,1),%edx
>   4:	38 d0                	cmp    %dl,%al
>   6:	7c 08                	jl     0x10
>   8:	84 d2                	test   %dl,%dl
>   a:	0f 85 b4 10 00 00    	jne    0x10c4
>  10:	44 8b 05 b8 11 7a 05 	mov    0x57a11b8(%rip),%r8d        > 0x57a11cf
>  17:	45 85 c0             	test   %r8d,%r8d
>  1a:	75 13                	jne    0x2f
>  1c:	48 8d 3d 9c 16 7d 05 	lea    0x57d169c(%rip),%rdi        > 0x57d16bf
>  23:	48 c7 c6 80 d3 ef 8b 	mov    $0xffffffff8befd380,%rsi
>* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
>  2f:	90                   	nop
>  30:	e9 1b f8 ff ff       	jmp    0xfffff850
>  35:	4d 8d a7 f0 0a 00 00 	lea    0xaf0(%r15),%r12
>  3c:	4c 89 e7             	mov    %r12,%rdi
>  3f:	e8                   	.byte 0xe8

I believe this is a extension of this crash[1]. Would consider marking it as invalid
as it is a user-unreachable path said by Greg KH here[2]

[1]: https://lore.kernel.org/all/6a8c451c.dbb3a75c.7844.0004.GAE@xxxxxxxxxx/T/
[2]: https://lore.kernel.org/all/2026082737-traitor-shorter-a4cc@gregkh/

Thanks,
Jeffin.