From: Hillf Danton <hdanton@sina.com>
To: syzbot <syzbot+b5d7ab56d43de3fd5aac@syzkaller.appspotmail.com>
Cc: dmitry.torokhov@gmail.com, linux-input@vger.kernel.org,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [input?] possible deadlock in tasklet_action_common (2)
Date: Thu, 21 May 2026 09:52:32 +0800 [thread overview]
Message-ID: <20260521015233.873-1-hdanton@sina.com> (raw)
In-Reply-To: <6a0de9e2.050a0220.18b3cb.000d.GAE@google.com>
> Date: Wed, 20 May 2026 10:05:38 -0700 [thread overview]
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: e98d21c170b0 Add linux-next specific files for 20260508
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1354bfce580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=59b98218d9b2edf4
> dashboard link: https://syzkaller.appspot.com/bug?extid=b5d7ab56d43de3fd5aac
> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/66f2a00ee290/disk-e98d21c1.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6b982257ce9e/vmlinux-e98d21c1.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a73fbea43e1a/bzImage-e98d21c1.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b5d7ab56d43de3fd5aac@syzkaller.appspotmail.com
>
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Tainted: G L
> ------------------------------------------------------
> syz.2.4328/32663 is trying to acquire lock:
> ffff8880b8724168 (tasklet_sync_callback.cb_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
> ffff8880b8724168 (tasklet_sync_callback.cb_lock){+...}-{3:3}, at: tasklet_lock_callback kernel/softirq.c:881 [inline]
> ffff8880b8724168 (tasklet_sync_callback.cb_lock){+...}-{3:3}, at: tasklet_action_common+0xc5/0x610 kernel/softirq.c:931
>
> but task is already holding lock:
> ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
> ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: class_spinlock_irqsave_constructor include/linux/spinlock.h:619 [inline]
> ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: input_inject_event+0xa4/0x320 drivers/input/input.c:419
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&dev->event_lock#2){+.+.}-{3:3}:
> rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
> spin_lock include/linux/spinlock_rt.h:45 [inline]
> class_spinlock_irqsave_constructor include/linux/spinlock.h:619 [inline]
> input_inject_event+0xa4/0x320 drivers/input/input.c:419
> led_trigger_event+0x13b/0x220 drivers/leds/led-triggers.c:420
> kbd_propagate_led_state drivers/tty/vt/keyboard.c:1118 [inline]
> kbd_bh+0x1b4/0x2c0 drivers/tty/vt/keyboard.c:1297
> tasklet_action_common+0x31c/0x610 kernel/softirq.c:942
> handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
> __do_softirq kernel/softirq.c:660 [inline]
> run_ktimerd+0x69/0x100 kernel/softirq.c:1155
> smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
> kthread+0x388/0x470 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
>
Deadlock if the timer thread is preempted
timer thread
tasklet_sync_callback.cb_lock
// preempted
&dev->event_lock
do softirq
acquire tasklet_sync_callback.cb_lock
acquire &dev->event_lock
> -> #0 (tasklet_sync_callback.cb_lock){+...}-{3:3}:
> check_prev_add kernel/locking/lockdep.c:3167 [inline]
> check_prevs_add kernel/locking/lockdep.c:3286 [inline]
> validate_chain kernel/locking/lockdep.c:3910 [inline]
> __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
> lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
> rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
> spin_lock include/linux/spinlock_rt.h:45 [inline]
> tasklet_lock_callback kernel/softirq.c:881 [inline]
> tasklet_action_common+0xc5/0x610 kernel/softirq.c:931
> handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
> __do_softirq kernel/softirq.c:660 [inline]
> __local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
> local_bh_enable include/linux/bottom_half.h:33 [inline]
> __alloc_skb+0x1aa/0x7d0 net/core/skbuff.c:697
> alloc_skb include/linux/skbuff.h:1381 [inline]
> hidp_send_message+0xb5/0x230 net/bluetooth/hidp/core.c:111
> hidp_send_intr_message net/bluetooth/hidp/core.c:143 [inline]
> hidp_input_event+0x2a4/0x380 net/bluetooth/hidp/core.c:175
> input_event_dispose+0x80/0x6b0 drivers/input/input.c:322
> input_inject_event+0x1d7/0x320 drivers/input/input.c:424
> kbd_led_trigger_activate+0xbc/0x100 drivers/tty/vt/keyboard.c:1074
> led_trigger_set+0x53b/0x960 drivers/leds/led-triggers.c:220
> led_match_default_trigger drivers/leds/led-triggers.c:277 [inline]
> led_trigger_set_default+0x266/0x2a0 drivers/leds/led-triggers.c:300
> led_classdev_register_ext+0x787/0x9c0 drivers/leds/led-class.c:581
> led_classdev_register include/linux/leds.h:274 [inline]
> input_leds_connect+0x517/0x790 drivers/input/input-leds.c:145
> input_attach_handler drivers/input/input.c:1011 [inline]
> input_register_device+0xce0/0x1140 drivers/input/input.c:2395
> hidp_session_dev_add net/bluetooth/hidp/core.c:861 [inline]
> hidp_session_probe+0x1a5/0x8a0 net/bluetooth/hidp/core.c:1139
> l2cap_register_user+0xc2/0x1d0 net/bluetooth/l2cap_core.c:1725
> hidp_connection_add+0x158b/0x1a20 net/bluetooth/hidp/core.c:1411
> do_hidp_sock_ioctl net/bluetooth/hidp/sock.c:81 [inline]
> hidp_sock_ioctl+0x403/0x650 net/bluetooth/hidp/sock.c:128
> sock_do_ioctl+0x101/0x320 net/socket.c:1328
> sock_ioctl+0x5c9/0x7f0 net/socket.c:1449
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:597 [inline]
> __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&dev->event_lock#2);
> lock(tasklet_sync_callback.cb_lock);
> lock(&dev->event_lock#2);
> lock(tasklet_sync_callback.cb_lock);
>
> *** DEADLOCK ***
>
> 10 locks held by syz.2.4328/32663:
> #0: ffff88805ebb3370 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_register_user+0x35/0x1d0 net/bluetooth/l2cap_core.c:1712
> #1: ffffffff8f73d960 (hidp_session_sem){++++}-{4:4}, at: hidp_session_probe+0x98/0x8a0 net/bluetooth/hidp/core.c:1129
> #2: ffffffff8f006e58 (input_mutex){+.+.}-{4:4}, at: class_mutex_intr_constructor include/linux/mutex.h:255 [inline]
> #2: ffffffff8f006e58 (input_mutex){+.+.}-{4:4}, at: input_register_device+0xa56/0x1140 drivers/input/input.c:2391
> #3: ffff8880125ea860 (&led_cdev->led_access){+.+.}-{4:4}, at: led_classdev_register_ext+0x484/0x9c0 drivers/leds/led-class.c:539
> #4: ffffffff8e9c4400 (triggers_list_lock){++++}-{4:4}, at: led_trigger_set_default+0x77/0x2a0 drivers/leds/led-triggers.c:297
> #5: ffff8880125ea788 (&led_cdev->trigger_lock){+.+.}-{4:4}, at: led_trigger_set_default+0x87/0x2a0 drivers/leds/led-triggers.c:298
> #6: ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
> #6: ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: class_spinlock_irqsave_constructor include/linux/spinlock.h:619 [inline]
> #6: ffff888058598270 (&dev->event_lock#2){+.+.}-{3:3}, at: input_inject_event+0xa4/0x320 drivers/input/input.c:419
> #7: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
> #7: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
> #7: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
> #7: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
> #8: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
> #8: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
> #8: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1181 [inline]
> #8: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: input_inject_event+0xb0/0x320 drivers/input/input.c:420
> #9: ffffffff8e1c8240 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
>
> stack backtrace:
> CPU: 1 UID: 0 PID: 32663 Comm: syz.2.4328 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
> Tainted: [L]=SOFTLOCKUP
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
> Call Trace:
> <TASK>
> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
> print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2045
> check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2177
> check_prev_add kernel/locking/lockdep.c:3167 [inline]
> check_prevs_add kernel/locking/lockdep.c:3286 [inline]
> validate_chain kernel/locking/lockdep.c:3910 [inline]
> __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
> lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
> rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
> spin_lock include/linux/spinlock_rt.h:45 [inline]
> tasklet_lock_callback kernel/softirq.c:881 [inline]
> tasklet_action_common+0xc5/0x610 kernel/softirq.c:931
> handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
> __do_softirq kernel/softirq.c:660 [inline]
> __local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
> local_bh_enable include/linux/bottom_half.h:33 [inline]
> __alloc_skb+0x1aa/0x7d0 net/core/skbuff.c:697
> alloc_skb include/linux/skbuff.h:1381 [inline]
> hidp_send_message+0xb5/0x230 net/bluetooth/hidp/core.c:111
> hidp_send_intr_message net/bluetooth/hidp/core.c:143 [inline]
> hidp_input_event+0x2a4/0x380 net/bluetooth/hidp/core.c:175
> input_event_dispose+0x80/0x6b0 drivers/input/input.c:322
> input_inject_event+0x1d7/0x320 drivers/input/input.c:424
> kbd_led_trigger_activate+0xbc/0x100 drivers/tty/vt/keyboard.c:1074
> led_trigger_set+0x53b/0x960 drivers/leds/led-triggers.c:220
> led_match_default_trigger drivers/leds/led-triggers.c:277 [inline]
> led_trigger_set_default+0x266/0x2a0 drivers/leds/led-triggers.c:300
> led_classdev_register_ext+0x787/0x9c0 drivers/leds/led-class.c:581
> led_classdev_register include/linux/leds.h:274 [inline]
> input_leds_connect+0x517/0x790 drivers/input/input-leds.c:145
> input_attach_handler drivers/input/input.c:1011 [inline]
> input_register_device+0xce0/0x1140 drivers/input/input.c:2395
> hidp_session_dev_add net/bluetooth/hidp/core.c:861 [inline]
> hidp_session_probe+0x1a5/0x8a0 net/bluetooth/hidp/core.c:1139
> l2cap_register_user+0xc2/0x1d0 net/bluetooth/l2cap_core.c:1725
> hidp_connection_add+0x158b/0x1a20 net/bluetooth/hidp/core.c:1411
> do_hidp_sock_ioctl net/bluetooth/hidp/sock.c:81 [inline]
> hidp_sock_ioctl+0x403/0x650 net/bluetooth/hidp/sock.c:128
> sock_do_ioctl+0x101/0x320 net/socket.c:1328
> sock_ioctl+0x5c9/0x7f0 net/socket.c:1449
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:597 [inline]
> __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fcb5e6cce59
> 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:00007fcb5c905028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fcb5e946090 RCX: 00007fcb5e6cce59
> RDX: 00002000000000c0 RSI: 00000000400448c8 RDI: 0000000000000009
> RBP: 00007fcb5e762d6f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fcb5e946128 R14: 00007fcb5e946090 R15: 00007ffddb8adae8
> </TASK>
next prev parent reply other threads:[~2026-05-21 1:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 17:05 [syzbot] [input?] possible deadlock in tasklet_action_common (2) syzbot
2026-05-21 1:52 ` Hillf Danton [this message]
2026-05-21 14:34 ` Sebastian Andrzej Siewior
2026-05-21 22:35 ` Hillf Danton
2026-05-22 6:39 ` Sebastian Andrzej Siewior
2026-05-22 7:21 ` Hillf Danton
2026-05-22 7:35 ` Sebastian Andrzej Siewior
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