From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from r3-21.sinamail.sina.com.cn (r3-21.sinamail.sina.com.cn [202.108.3.21]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D52AD346FA7 for ; Thu, 21 May 2026 22:35:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=202.108.3.21 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779402941; cv=none; b=JQDqkI8514graTOWKb3ZGmKN5DbVymNzmE4bNPIc72LAmpwbuqCWW0wDCixhlfA/vP94RcsqDzlm/4MwjX8vobAwIWMo7hEGNGe3sNIqayFFAkzdGIViEUNlJdH36QBQJwUYri/MA+BMCn9vJ1ukRMvP+d7OTeD0u02V7gaN5lw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779402941; c=relaxed/simple; bh=qdMfnvr8Z89+G6dY59XhDbSO49CTSZxRrv6V6wEkSzo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; 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<20260521143414.P7XZgsrN@linutronix.de> References: Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Thu, 21 May 2026 16:34:14 +0200 Sebastian Andrzej Siewior wrote: >On 2026-05-21 09:52:32 [+0800], Hillf Danton wrote: >> > 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 > > This is obvious and looks fine. > >> 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 > > This shouldn't happen. > >> > -> #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 > > up to kbd_led_trigger_activate(), I can follow. In > kbd_led_trigger_activate() it disables the keyboard tasklet and then > does led_set_brightness(). Not sure how it ends up in > input_inject_event(). > input_inject_event() is invoked in the brightness_set callback [1] for example. [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/input/input-leds.c#n142 > Now, input_inject_event() does spin_lock_irqsave() and alloc_skb() does > local_bh_disable()/ local_bh_enable(). On !RT this is not legal. On RT Can you please specify why that is illegal on !RT? > it is okay but then local_bh_enable() here should not invoke any > softirqs because none were raised within the section (alloc_skb()). On RT spinlock is replaced with mutex, and softirq can be raised in the irq that could come any moment after spin_lock_irqsave(). > Not sure if this really did occur as such or lockdep comes with the > shortest backtrace based on the lockclass and this is it. > >> > 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 > >Sebastian