From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 32E541DDE9; Fri, 1 Dec 2023 09:55:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OM2qwCtq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B088C433C9; Fri, 1 Dec 2023 09:54:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701424501; bh=bfdACYLcpe5G5L0M6AML9A5cua2JX5r67pEzdtiedpg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OM2qwCtqmy0HGBIU7FzC2dum9gSWAJTUBmZo7ezgnnkLNhs37nOT2dDuUK/FIF8I4 mGkwd/lGcEwDQJPrb/3K3t4VMPda5s5WglnPeMQy3gLu8Qg6ubXqxYx7edDZ/J0Rec RK51Ff/+rCzMzqdb5M0TIPaw6PBQX5d1jlRtBmTCjFjJG73cT79e3kMZS87MCUCko2 QZOBWEz1+Ljk7A58EKLpWxdsddEUcmP9lOfi3xkEnFOUExR32PYsp05NkJQlgVqQ16 nc2WlDcYLxMo84mmFUkY7nFFFIjNTY/8m90CzhE2AjWXv6WObo8MBsNyXJy+ZqIkBo eTJl13jJZgSAw== Date: Fri, 1 Dec 2023 09:54:55 +0000 From: Simon Horman To: Heiner Kallweit Cc: Christian Marangi , Pavel Machek , Lee Jones , Jakub Kicinski , Andrew Lunn , "linux-leds@vger.kernel.org" , "netdev@vger.kernel.org" Subject: Re: [PATCH] leds: trigger: netdev: fix RTNL handling to prevent potential deadlock Message-ID: <20231201095455.GS32077@kernel.org> References: <7cfd7a10-53d4-45a8-908c-39459b1f8b1a@gmail.com> Precedence: bulk X-Mailing-List: linux-leds@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7cfd7a10-53d4-45a8-908c-39459b1f8b1a@gmail.com> On Wed, Nov 29, 2023 at 09:03:56AM +0100, Heiner Kallweit wrote: > When working on LED support for r8169 I got the following lockdep > warning. Easiest way to prevent this scenario seems to be to take > the RTNL lock before the trigger_data lock in set_device_name(). > > ====================================================== > WARNING: possible circular locking dependency detected > 6.7.0-rc2-next-20231124+ #2 Not tainted > ------------------------------------------------------ > bash/383 is trying to acquire lock: > ffff888103aa1c68 (&trigger_data->lock){+.+.}-{3:3}, at: netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > > but task is already holding lock: > ffffffff8cddf808 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x12/0x20 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (rtnl_mutex){+.+.}-{3:3}: > __mutex_lock+0x9b/0xb50 > mutex_lock_nested+0x16/0x20 > rtnl_lock+0x12/0x20 > set_device_name+0xa9/0x120 [ledtrig_netdev] > netdev_trig_activate+0x1a1/0x230 [ledtrig_netdev] > led_trigger_set+0x172/0x2c0 > led_trigger_write+0xf1/0x140 > sysfs_kf_bin_write+0x5d/0x80 > kernfs_fop_write_iter+0x15d/0x210 > vfs_write+0x1f0/0x510 > ksys_write+0x6c/0xf0 > __x64_sys_write+0x14/0x20 > do_syscall_64+0x3f/0xf0 > entry_SYSCALL_64_after_hwframe+0x6c/0x74 > > -> #0 (&trigger_data->lock){+.+.}-{3:3}: > __lock_acquire+0x1459/0x25a0 > lock_acquire+0xc8/0x2d0 > __mutex_lock+0x9b/0xb50 > mutex_lock_nested+0x16/0x20 > netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > call_netdevice_register_net_notifiers+0x5a/0x100 > register_netdevice_notifier+0x85/0x120 > netdev_trig_activate+0x1d4/0x230 [ledtrig_netdev] > led_trigger_set+0x172/0x2c0 > led_trigger_write+0xf1/0x140 > sysfs_kf_bin_write+0x5d/0x80 > kernfs_fop_write_iter+0x15d/0x210 > vfs_write+0x1f0/0x510 > ksys_write+0x6c/0xf0 > __x64_sys_write+0x14/0x20 > do_syscall_64+0x3f/0xf0 > entry_SYSCALL_64_after_hwframe+0x6c/0x74 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(rtnl_mutex); > lock(&trigger_data->lock); > lock(rtnl_mutex); > lock(&trigger_data->lock); > > *** DEADLOCK *** > > 8 locks held by bash/383: > #0: ffff888103ff33f0 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x6c/0xf0 > #1: ffff888103aa1e88 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x114/0x210 > #2: ffff8881036f1890 (kn->active#82){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x11d/0x210 > #3: ffff888108e2c358 (&led_cdev->led_access){+.+.}-{3:3}, at: led_trigger_write+0x30/0x140 > #4: ffffffff8cdd9e10 (triggers_list_lock){++++}-{3:3}, at: led_trigger_write+0x75/0x140 > #5: ffff888108e2c270 (&led_cdev->trigger_lock){++++}-{3:3}, at: led_trigger_write+0xe3/0x140 > #6: ffffffff8cdde3d0 (pernet_ops_rwsem){++++}-{3:3}, at: register_netdevice_notifier+0x1c/0x120 > #7: ffffffff8cddf808 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x12/0x20 > > stack backtrace: > CPU: 0 PID: 383 Comm: bash Not tainted 6.7.0-rc2-next-20231124+ #2 > Hardware name: Default string Default string/Default string, BIOS ADLN.M6.SODIMM.ZB.CY.015 08/08/2023 > Call Trace: > > dump_stack_lvl+0x5c/0xd0 > dump_stack+0x10/0x20 > print_circular_bug+0x2dd/0x410 > check_noncircular+0x131/0x150 > __lock_acquire+0x1459/0x25a0 > lock_acquire+0xc8/0x2d0 > ? netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > __mutex_lock+0x9b/0xb50 > ? netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > ? __this_cpu_preempt_check+0x13/0x20 > ? netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > ? __cancel_work_timer+0x11c/0x1b0 > ? __mutex_lock+0x123/0xb50 > mutex_lock_nested+0x16/0x20 > ? mutex_lock_nested+0x16/0x20 > netdev_trig_notify+0xec/0x190 [ledtrig_netdev] > call_netdevice_register_net_notifiers+0x5a/0x100 > register_netdevice_notifier+0x85/0x120 > netdev_trig_activate+0x1d4/0x230 [ledtrig_netdev] > led_trigger_set+0x172/0x2c0 > ? preempt_count_add+0x49/0xc0 > led_trigger_write+0xf1/0x140 > sysfs_kf_bin_write+0x5d/0x80 > kernfs_fop_write_iter+0x15d/0x210 > vfs_write+0x1f0/0x510 > ksys_write+0x6c/0xf0 > __x64_sys_write+0x14/0x20 > do_syscall_64+0x3f/0xf0 > entry_SYSCALL_64_after_hwframe+0x6c/0x74 > RIP: 0033:0x7f269055d034 > Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d 35 c3 0d 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 48 83 ec 28 48 89 54 24 18 48 > RSP: 002b:00007ffddb7ef748 EFLAGS: 00000202 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 0000000000000007 RCX: 00007f269055d034 > RDX: 0000000000000007 RSI: 000055bf5f4af3c0 RDI: 0000000000000001 > RBP: 000055bf5f4af3c0 R08: 0000000000000073 R09: 0000000000000001 > R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000007 > R13: 00007f26906325c0 R14: 00007f269062ff20 R15: 0000000000000000 > > > Fixes: f42c437acc55 ("leds: trigger: netdev: add additional specific link speed mode") Hi Heiner, The hash above doesn't seem to match what is upstream. Perhaps it should be: Fixes: d5e01266e7f5 ("leds: trigger: netdev: add additional specific link speed mode") > Signed-off-by: Heiner Kallweit ...