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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shiji Yang Subject: [BUG] AB-BA deadlock between net and led-trigger module Date: Sat, 21 Feb 2026 18:01:46 +0800 Message-ID: X-Mailer: git-send-email 2.51.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: SI2PR02CA0008.apcprd02.prod.outlook.com (2603:1096:4:194::12) To OS7PR01MB13602.jpnprd01.prod.outlook.com (2603:1096:604:359::9) X-Microsoft-Original-Message-ID: <20260221100146.3997405-1-yangshiji66@outlook.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: OS7PR01MB13602:EE_|OSCPR01MB14596:EE_ X-MS-Office365-Filtering-Correlation-Id: 02f83435-e509-4f53-e579-08de71304555 X-MS-Exchange-SLBlob-MailProps: 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 X-Microsoft-Antispam: BCL:0;ARA:14566002|5072599009|461199028|15080799012|8060799015|19110799012|41001999006|23021999003|10035399007|440099028|3412199025|40105399003|52005399003|1710799026; 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After further tracking, this is caused by a AB-BA deadlock which can be reproduced in at least 5.15, 6.6, 6.12 and latest 6.18 LTS kenrel. Stack tracing on 6.12 kernel: ``` Task1 "netifd" is used to start/restart the network: [ 1361.967916] task:netifd state:D stack:0 pid:4743 tgid:4743 ppid:1 flags:0x08100000 [ 1361.977269] Stack : 00000001 00000001 00000006 800bf464 817a0cb0 800b67ac 00000001 83261b20 [ 1361.985668] 83261a54 00000000 83261aac 000007ef 00000000 80c04d74 00000000 00000002 [ 1361.994138] 83aba760 80ce0000 83261af8 00000002 83261af8 80cd0000 00000002 80d8058c [ 1362.002582] 80cc0000 809bae70 00000002 80d80000 80cd0000 80d80568 00000001 00000000 [ 1362.011033] 809baecc 83261af8 00000002 80d80560 80d80568 809bb11c 809c09c8 806614d0 [ 1362.019484] ... [ 1362.021942] Call Trace: [ 1362.024380] [<809ba6fc>] __schedule+0x504/0xc28 [ 1362.028974] [<809bae70>] schedule+0x50/0x190 [ 1362.033251] [<809bb11c>] schedule_preempt_disabled+0x1c/0x34 [ 1362.038958] [<809c0b94>] rwsem_down_write_slowpath+0x240/0x7f8 [ 1362.044789] [<809c11c0>] down_write+0x74/0x90 [ 1362.049207] [<8054e4b8>] led_trigger_register+0x5c/0x1fc <-- Trying to get lock "triggers_list_lock" via down_write(&triggers_list_lock); [ 1362.054536] [<80662830>] phy_led_triggers_register+0xd0/0x234 [ 1362.060329] [<8065e200>] phy_attach_direct+0x33c/0x40c [ 1362.065489] [<80651fc4>] phylink_fwnode_phy_connect+0x15c/0x23c [ 1362.071480] [<8066ee18>] mtk_open+0x7c/0xba0 [ 1362.075849] [<806d714c>] __dev_open+0x280/0x2b0 [ 1362.080384] [<806d7668>] __dev_change_flags+0x244/0x24c [ 1362.085598] [<806d7698>] dev_change_flags+0x28/0x78 [ 1362.090528] [<807150e4>] dev_ioctl+0x4c0/0x654 <-- Hold lock "rtnl_mutex" by calling rtnl_lock(); [ 1362.094985] [<80694360>] sock_ioctl+0x2f4/0x4e0 [ 1362.099567] [<802e9c4c>] sys_ioctl+0x32c/0xd8c [ 1362.104022] [<80014504>] syscall_common+0x34/0x58 Task2 "led" is used to set the led-trigger "netdev" for a GPIO LED: [ 1362.110308] task:led state:D stack:0 pid:4943 tgid:4943 ppid:1 flags:0x08100002 [ 1362.119656] Stack : 809bf818 80ce3ce4 80d47fa8 fffff000 00000000 809bf840 00000001 800bb264 [ 1362.128115] 00000000 00000000 80ce0000 80ce0000 00000000 80c04d7c 00000000 00000002 [ 1362.136565] 83b50d20 80ce0000 834e1cec 80d8c750 00000002 80cd7380 80da5f2c 00000000 [ 1362.144962] 00000000 809bae70 00000000 00000000 80d8c750 80d8c750 00000001 00000000 [ 1362.153412] 809baecc 00000002 80cd7380 80d8c74c 00000000 809bb11c 00000000 834e1cec [ 1362.161868] ... [ 1362.164327] Call Trace: [ 1362.166835] [<809ba6fc>] __schedule+0x504/0xc28 [ 1362.171385] [<809bae70>] schedule+0x50/0x190 [ 1362.175651] [<809bb11c>] schedule_preempt_disabled+0x1c/0x34 [ 1362.181361] [<809bdd48>] __mutex_lock+0x310/0x940 [ 1362.186132] [<809be394>] mutex_lock_nested+0x1c/0x28 [ 1362.191101] [<806c2640>] register_netdevice_notifier+0x60/0x168 <-- Trying to get lock "rtnl_mutex" via rtnl_lock(); [ 1362.197073] [<805504ac>] netdev_trig_activate+0x194/0x1e4 [ 1362.202490] [<8054e28c>] led_trigger_set+0x1d4/0x360 <-- Hold lock "triggers_list_lock" by down_read(&triggers_list_lock); [ 1362.207511] [<8054eb38>] led_trigger_write+0xd8/0x14c [ 1362.212566] [<80381d98>] sysfs_kf_bin_write+0x80/0xbc [ 1362.217688] [<8037fcd8>] kernfs_fop_write_iter+0x17c/0x28c [ 1362.223174] [<802cbd70>] vfs_write+0x21c/0x3c4 [ 1362.227712] [<802cc0c4>] ksys_write+0x78/0x12c [ 1362.232164] [<80014504>] syscall_common+0x34/0x58 ``` When the above two tasks are created at the same time, there is a probability that it will cause the network and LED to fail to initialize. [1] https://github.com/openwrt/openwrt/issues/18472 Regards, Shiji Yang