From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 88F47481A97; Sat, 12 Sep 2026 19:14:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789240494; cv=none; b=rWcuIT1dUEj42R/OnCkMUdROi2iVGB0gcZwu1CviXldXnAGJLTz1za6Z0N6X7c+Bfrk/CZ+K6jgHmD4nw4Ml5F2Jfdoqy8vHgTL8l8yoBuUGff0VhOFVOBwhbkzbtVNa6mraowz8K387RuFnG2SHc16Hss6BTzWYk/QyV1rRYbk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789240494; c=relaxed/simple; bh=1aW6GlRb+mfP0OwjBe6OX0XzrfDrJV4t+G1+HbMR9FY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rVYXMoeNWr//y4Vvr/FJssDibcjVu26pjkj3rpwNpFaXQkbVziGYrXsfLaAn9qlPPT7Jtk286LtlDA8YgXXeerLF2Fcc3pLToID9Ff6k6Xadc3qTszO6v8YzXTgSmgiCT19G6dPW3gJ79cvAnANjktEQEuk+gwDNW4T3IhEUo34= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GkGCeEOk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GkGCeEOk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2359A1F000FF; Sat, 12 Sep 2026 19:14:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789240493; bh=0DKysV5K5aMVsRF48PKwORfk1uDTRDxdeGjqFboJz+c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GkGCeEOk65mh3vPvRoyJz/WhUedDB+d4TMwVk9TC5MR0Ufe97Jv2WARY+xzio2hbU +Kk9+JC/7HSKBdM3W5/GW8/dll8Ki4uUNDtYimJs9nP84Ho370VYOtUpA8NNtm4ZL1 sqnuTFIm7G44hujgxAgD8gTL709MeQ6XOxig9Ttk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Pauli Virtanen , Luiz Augusto von Dentz , Sasha Levin Subject: [PATCH 5.15 880/935] Bluetooth: 6lowpan: fix cyclic locking warning on netdev unregister Date: Sat, 12 Sep 2026 09:05:10 +0200 Message-ID: <20260912065546.998506812@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065526.833703348@linuxfoundation.org> References: <20260912065526.833703348@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pauli Virtanen [ Upstream commit 9707a015fe8f3ba8ec7c270f3b2b8efb38823d6b ] 6lowpan.c has theoretically conflicting lock orderings, which lockdep complains about: a) rtnl_lock > hdev->workqueue from 6lowpan.c:delete_netdev -> rtnl_lock -> device_del -> put_device(parent) -> hci_release_dev -> destroy_workqueue b) hdev->workqueue > l2cap_conn->lock > chan->lock > rtnl_lock from hci_rx_work -> 6lowpan.c:chan_ready_cb -> lowpan_register_netdev, ifup -> rtnl_lock Actual deadlock appears not possible, as hci_rx_work is disabled and l2cap_conn flushed already on hdev unregister. Hence, do minimal thing to make lockdep happy by breaking chain a) by holding hdev refcount until after netdev put in 6lowpan.c. Fixes the lockdep complaint: WARNING: possible circular locking dependency detected. kworker/0:1/11 is trying to acquire lock: ffff8880023b3940 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x8b/0x130 but task is already holding lock: ffffffff95e4f9c0 (rtnl_mutex){+.+.}-{4:4}, at: lowpan_unregister_netdev+0xd/0x30 Workqueue: events delete_netdev Signed-off-by: Pauli Virtanen Signed-off-by: Luiz Augusto von Dentz Stable-dep-of: d4bfa78fd679 ("Bluetooth: L2CAP: reject accept queue add unless BT_LISTEN") Signed-off-by: Sasha Levin --- net/bluetooth/6lowpan.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c index d0b1882f5b4b7..72306b8d9c290 100644 --- a/net/bluetooth/6lowpan.c +++ b/net/bluetooth/6lowpan.c @@ -758,13 +758,33 @@ static inline struct l2cap_chan *chan_new_conn_cb(struct l2cap_chan *pchan) return chan; } +static void unregister_dev(struct lowpan_btle_dev *dev) +{ + struct hci_dev *hdev = READ_ONCE(dev->hdev); + + /* If netdev holds last reference to hci_dev (its parent device), this + * leads to theoretical cyclic locking on lowpan_unregister_netdev: + * + * rtnl_lock -> put_device(parent) -> hci_release_dev -> + * destroy_workqueue -> hci_rx_work -> l2cap_recv_acldata -> + * chan_ready_cb -> ifup -> rtnl_lock + * + * However, hci_rx_work is disabled in hci_unregister_dev, so this + * should not occur. Make lockdep happy by postponing hdev release after + * netdev put. + */ + hci_dev_hold(hdev); + lowpan_unregister_netdev(dev->netdev); + hci_dev_put(hdev); +} + static void delete_netdev(struct work_struct *work) { struct lowpan_btle_dev *entry = container_of(work, struct lowpan_btle_dev, delete_netdev); - lowpan_unregister_netdev(entry->netdev); + unregister_dev(entry); /* The entry pointer is deleted by the netdev destructor. */ } @@ -1232,6 +1252,7 @@ static void disconnect_devices(void) break; new_dev->netdev = entry->netdev; + new_dev->hdev = entry->hdev; INIT_LIST_HEAD(&new_dev->list); list_add_rcu(&new_dev->list, &devices); @@ -1243,7 +1264,7 @@ static void disconnect_devices(void) ifdown(entry->netdev); BT_DBG("Unregistering netdev %s %p", entry->netdev->name, entry->netdev); - lowpan_unregister_netdev(entry->netdev); + unregister_dev(entry); kfree(entry); } } -- 2.53.0