[syzbot] [media?] WARNING in as102_dvb_dmx_start_feed

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bbeb83d3182a Merge tag 'kbuild-fixes-7.0-3' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136f4772580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6754c86e8d9e4c91
dashboard link: https://syzkaller.appspot.com/bug?extid=3825a6102073c418fe41
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=176e7af6580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16754b52580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dbd3eaf2f899/disk-bbeb83d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/45838a797bcf/vmlinux-bbeb83d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ba91cdcacfe1/bzImage-bbeb83d3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3825a6...@syzkaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(lock->magic != lock)
WARNING: kernel/locking/mutex.c:593 at __mutex_lock_common kernel/locking/mutex.c:593 [inline], CPU#1: syz.2.23/6152
WARNING: kernel/locking/mutex.c:593 at __mutex_lock+0x10a4/0x1300 kernel/locking/mutex.c:776, CPU#1: syz.2.23/6152
Modules linked in:
CPU: 1 UID: 0 PID: 6152 Comm: syz.2.23 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:593 [inline]
RIP: 0010:__mutex_lock+0x10ab/0x1300 kernel/locking/mutex.c:776
Code: 11 90 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 33 02 00 00 83 3d d9 a1 61 04 00 75 13 48 8d 3d 1c b7 64 04 48 c7 c6 c0 e0 cc 8b <67> 48 0f b9 3a 90 e9 ac f0 ff ff 90 0f 0b 90 e9 73 f4 ff ff 90 0f
RSP: 0018:ffffc90003917a20 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 1ffff92000722f5c RCX: ffff88807c728000
RDX: 0000000000000000 RSI: ffffffff8bcce0c0 RDI: ffffffff9014fc10
RBP: ffffc90003917bd8 R08: ffffffff9011e6c3 R09: 1ffffffff2023cd8
R10: dffffc0000000000 R11: fffffbfff2023cd9 R12: ffff88807e2e2b60
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00005555608ec500(0000) GS:ffff88812555d000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2fb63fff CR3: 000000007e05c000 CR4: 00000000003526f0
Call Trace:
<TASK>
as102_dvb_dmx_start_feed+0x70/0x290 drivers/media/usb/as102/as102_drv.c:139
dmx_section_feed_start_filtering+0x518/0x6c0 drivers/media/dvb-core/dvb_demux.c:977
dvb_dmxdev_filter_start+0xcf4/0x10e0 drivers/media/dvb-core/dmxdev.c:760
dvb_demux_do_ioctl+0x470/0x540 drivers/media/dvb-core/dmxdev.c:1083
dvb_usercopy+0x199/0x2e0 drivers/media/dvb-core/dvbdev.c:996
dvb_demux_ioctl+0x29/0x40 drivers/media/dvb-core/dmxdev.c:1201
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9a3979c799
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:00007ffef627ed38 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9a39a15fa0 RCX: 00007f9a3979c799
RDX: 0000200000000200 RSI: 00000000403c6f2b RDI: 0000000000000004
RBP: 00007f9a39832c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9a39a15fac R14: 00007f9a39a15fa0 R15: 00007f9a39a15fa0
</TASK>
----------------
Code disassembly (best guess):
0: 11 90 48 c1 e8 03 adc %edx,0x3e8c148(%rax)
6: 42 0f b6 04 28 movzbl (%rax,%r13,1),%eax
b: 84 c0 test %al,%al
d: 0f 85 33 02 00 00 jne 0x246
13: 83 3d d9 a1 61 04 00 cmpl $0x0,0x461a1d9(%rip) # 0x461a1f3
1a: 75 13 jne 0x2f
1c: 48 8d 3d 1c b7 64 04 lea 0x464b71c(%rip),%rdi # 0x464b73f
23: 48 c7 c6 c0 e0 cc 8b mov $0xffffffff8bcce0c0,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 90 nop
30: e9 ac f0 ff ff jmp 0xfffff0e1
35: 90 nop
36: 0f 0b ud2
38: 90 nop
39: e9 73 f4 ff ff jmp 0xfffff4b1
3e: 90 nop
3f: 0f .byte 0xf


---
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If the report is already addressed, let syzbot know by replying with:
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[Edward Adam Davis]

#syz test

diff --git a/drivers/media/usb/as102/as102_drv.c b/drivers/media/usb/as102/as102_drv.c
index 6b1d3528a0a7..e94828871635 100644
--- a/drivers/media/usb/as102/as102_drv.c
+++ b/drivers/media/usb/as102/as102_drv.c
@@ -299,6 +299,8 @@ int as102_dvb_register(struct as102_dev_t *as102_dev)
as102_dev->dvb_dmx.priv = as102_dev;
as102_dev->dvb_dmx.filternum = pid_filtering ? 16 : 256;
as102_dev->dvb_dmx.feednum = 256;
+ /* init start / stop stream mutex */
+ mutex_init(&as102_dev->sem);
as102_dev->dvb_dmx.start_feed = as102_dvb_dmx_start_feed;
as102_dev->dvb_dmx.stop_feed = as102_dvb_dmx_stop_feed;

@@ -344,9 +346,6 @@ int as102_dvb_register(struct as102_dev_t *as102_dev)
/* init bus mutex for token locking */
mutex_init(&as102_dev->bus_adap.lock);

- /* init start / stop stream mutex */
- mutex_init(&as102_dev->sem);
-
/*
* try to load as102 firmware. If firmware upload failed, we'll be
* able to upload it later.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+3825a6...@syzkaller.appspotmail.com
Tested-by: syzbot+3825a6...@syzkaller.appspotmail.com

Tested on:

commit: 0138af24 Merge tag 'erofs-for-7.0-rc6-fixes' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e0aeda580000

kernel config: https://syzkaller.appspot.com/x/.config?x=6754c86e8d9e4c91
dashboard link: https://syzkaller.appspot.com/bug?extid=3825a6102073c418fe41
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=17628eda580000

Note: testing is done by a robot and is best-effort only.