[syzbot] [nfc?] kernel panic: kernel: panic_on_warn set ... (3)

[syzbot] [nfc?] kernel panic: kernel: panic_on_warn set ... (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f9a2394a2348 Merge tag 'mm-hotfixes-stable-2026-08-06-18-4..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11a1be49580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=30772517ee66ef58
dashboard link: https://syzkaller.appspot.com/bug?extid=fe5ea83cdd7fc263f452
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ebec1b22682a/disk-f9a2394a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5c88db273365/vmlinux-f9a2394a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/43600cc1b90a/bzImage-f9a2394a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fe5ea83cdd7fc263f452@syzkaller.appspotmail.com

Kernel panic - not syncing: kernel: panic_on_warn set ...
CPU: 0 UID: 0 PID: 7451 Comm: kworker/u8:11 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: iou_exit io_ring_exit_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 vpanic+0x552/0x970 kernel/panic.c:651
 panic+0xd1/0xe0 kernel/panic.c:788
 check_panic_on_warn kernel/panic.c:525 [inline]
 check_panic_on_warn.cold+0x19/0x34 kernel/panic.c:520
 __warn.cold+0x191/0x318 kernel/panic.c:1104
 __report_bug+0x30f/0x440 lib/bug.c:254
 report_bug+0xb2/0x220 lib/bug.c:286
 handle_bug+0x16a/0x2a0 arch/x86/kernel/traps.c:436
 exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:490
 asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:593
RIP: 0010:io_ring_exit_work+0x479/0xd7a io_uring/io_uring.c:2365
Code: 8e e8 ab 8c 44 01 48 8b 05 24 97 4b 0d 4c 8b 7c 24 38 31 ff 49 29 c7 4c 89 fe e8 f2 f2 d4 00 4d 85 ff 79 12 e8 48 f8 d4 00 90 <0f> 0b 90 48 c7 44 24 20 70 17 00 00 e8 36 f8 d4 00 48 8b 74 24 20
RSP: 0018:ffffc900047b7aa0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888052290710 RCX: ffffffff81355b6e
RDX: ffff888052140000 RSI: ffffffff81355b78 RDI: ffff888052140000
RBP: ffffc900047b7c38 R08: 0000000000000007 R09: 0000000000000000
R10: fffffffffffffffc R11: 0000000000000000 R12: ffff888052290000
R13: dffffc0000000000 R14: 0000000052290700 R15: fffffffffffffffc
 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
 process_scheduled_works kernel/workqueue.c:3405 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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Re: [syzbot] [bluetooth?] kernel panic: kernel: panic_on_warn set ... (3)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    08dbfad3f504 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14f47379580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
dashboard link: https://syzkaller.appspot.com/bug?extid=fe5ea83cdd7fc263f452
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c2a379580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16181e25580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ddff5719ec3b/disk-08dbfad3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4b5e39b20fa5/vmlinux-08dbfad3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eb1f70eed57f/bzImage-08dbfad3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fe5ea83cdd7fc263f452@syzkaller.appspotmail.com

 <TASK>
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Kernel panic - not syncing: kernel: panic_on_warn set ...
CPU: 1 UID: 0 PID: 5905 Comm: kworker/u9:5 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: hci5 hci_conn_timeout
Call Trace:
 <TASK>
 vpanic+0x56d/0xa60 kernel/panic.c:651
 panic+0xc5/0xd0 kernel/panic.c:788
 check_panic_on_warn kernel/panic.c:525 [inline]
 __warn+0x315/0x4c0 kernel/panic.c:1104
 __report_bug+0x276/0x570 lib/bug.c:254
 report_bug+0x16b/0x220 lib/bug.c:286
 handle_bug+0x9c/0x200 arch/x86/kernel/traps.c:436
 exc_invalid_op+0x1a/0x50 arch/x86/kernel/traps.c:490
 asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:593
RIP: 0010:hci_conn_timeout+0xff/0x2c0 net/bluetooth/hci_conn.c:641
Code: 48 89 df e8 e3 f5 09 00 eb 07 e8 ac 50 f1 f6 b0 13 0f b6 f0 48 89 df 5b 41 5c 41 5e 41 5f 5d e9 d7 9f fe ff e8 92 50 f1 f6 90 <0f> 0b 90 eb 8c 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 31 ff ff ff
RSP: 0018:ffffc90003097ab0 EFLAGS: 00010293
RAX: ffffffff8ad6630e RBX: ffff888079288000 RCX: ffff88802f728000
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: 0000000000000000
RBP: 00000000ffffffff R08: ffff888079288013 R09: 1ffff1100f251002
R10: dffffc0000000000 R11: ffffed100f251003 R12: dffffc0000000000
R13: ffffffff818f95da R14: ffff888079288a50 R15: ffff888079288010
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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.

Re: [syzbot] [bluetooth?] kernel panic: kernel: panic_on_warn set ... (3)

[Hillf Danton]

> Date: Sun, 30 Aug 2026 10:38:31 -0700	[thread overview]
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    08dbfad3f504 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14f47379580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
> dashboard link: https://syzkaller.appspot.com/bug?extid=fe5ea83cdd7fc263f452
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c2a379580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16181e25580000

#syz test

--- x/include/net/bluetooth/hci_core.h
+++ y/include/net/bluetooth/hci_core.h
@@ -1701,9 +1701,13 @@ static inline struct hci_conn *hci_conn_
 
 static inline void hci_conn_drop(struct hci_conn *conn)
 {
+	int cnt;
+
 	BT_DBG("hcon %p orig refcnt %d", conn, atomic_read(&conn->refcnt));
 
-	if (atomic_dec_and_test(&conn->refcnt)) {
+	cnt = atomic_dec_return(&conn->refcnt);
+	WARN_ON(cnt < 0);
+	if (cnt == 0) {
 		unsigned long timeo;
 
 		switch (conn->type) {
--

Re: [syzbot] [bluetooth?] kernel panic: kernel: panic_on_warn set ... (3)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in hci_conn_drop

------------[ cut here ]------------
cnt < 0
WARNING: ./include/net/bluetooth/hci_core.h:1709 at hci_conn_drop+0x1c5/0x2d0 include/net/bluetooth/hci_core.h:1709, CPU#1: kworker/u9:1/4935
Modules linked in:
CPU: 1 UID: 0 PID: 4935 Comm: kworker/u9:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: hci3 hci_cmd_sync_work
RIP: 0010:hci_conn_drop+0x1c5/0x2d0 include/net/bluetooth/hci_core.h:1709
Code: e7 e8 9f 49 4f f7 49 8b 34 24 bf 08 00 00 00 4c 89 fa 4c 89 f1 5b 41 5c 41 5d 41 5e 41 5f 5d e9 c1 08 a6 f6 e8 0c 80 df f6 90 <0f> 0b 90 e9 91 fe ff ff 44 89 f1 80 e1 07 38 c1 0f 8c b5 fe ff ff
RSP: 0018:ffffc9000f9f7a10 EFLAGS: 00010293
RAX: ffffffff8ae836a4 RBX: ffff88807fd9c000 RCX: ffff888033f63e80
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: 0000000000000000
RBP: 00000000ffffff92 R08: ffff88807fd9c013 R09: 1ffff1100ffb3802
R10: dffffc0000000000 R11: ffffed100ffb3803 R12: ffff88803255ea18
R13: 1ffff110064abd43 R14: 00000000ffffffff R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888124dda000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3acee37008 CR3: 000000007b2ae000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 le_read_features_complete+0x24/0xd0 net/bluetooth/hci_sync.c:7873
 hci_cmd_sync_work+0x25a/0x3f0 net/bluetooth/hci_sync.c:334
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         cee9395a Linux 7.3-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f2ec15580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5e4e3a0e188a497e
dashboard link: https://syzkaller.appspot.com/bug?extid=fe5ea83cdd7fc263f452
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=145a5379580000