From: Yang Li <yang.li@xxxxxxxxxxx> [ Upstream commit de5d7d3f27ddd4046736f558a40e252ddda82013 ] list_empty(&hdev->adv_instances) is always true during startup, so an advertising instance is added by default. Call trace: dump_backtrace+0x94/0xec show_stack+0x18/0x24 dump_stack_lvl+0x48/0x60 dump_stack+0x18/0x24 hci_setup_ext_adv_instance_sync+0x17c/0x328 hci_powered_update_adv_sync+0xb4/0x12c hci_powered_update_sync+0x54/0x70 hci_power_on_sync+0xe4/0x278 hci_set_powered_sync+0x28/0x34 set_powered_sync+0x40/0x58 hci_cmd_sync_work+0x94/0x100 process_one_work+0x168/0x444 worker_thread+0x378/0x3f4 kthread+0x108/0x10c ret_from_fork+0x10/0x20 Link: https://github.com/bluez/bluez/issues/1442 Signed-off-by: Yang Li <yang.li@xxxxxxxxxxx> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- LLM Generated explanations, may be completely bogus: **Backport Status: YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Bug Analysis The commit fixes a **logic error** in `hci_powered_update_adv_sync()` that causes unnecessary default advertising instance creation during Bluetooth startup. The problematic code at line 3290 uses an OR condition: ```c if (hci_dev_test_flag(hdev, HCI_ADVERTISING) || list_empty(&hdev->adv_instances)) ``` This condition is **always true** during startup because `list_empty(&hdev->adv_instances)` returns true when the advertising instances list is initially empty. This causes the code block to execute unconditionally, creating a default advertising instance even when not needed. ## The Fix The patch changes the OR (`||`) to AND (`&&`): ```c if (hci_dev_test_flag(hdev, HCI_ADVERTISING) && list_empty(&hdev->adv_instances)) ``` This ensures the default advertising setup only occurs when: 1. The HCI_ADVERTISING flag is explicitly set, AND 2. There are no advertising instances configured ## Why This Should Be Backported 1. **Clear Bug Fix**: This is a straightforward logic error that causes incorrect behavior during Bluetooth initialization. The stack trace in the commit message shows this happens during normal startup flow (`hci_power_on_sync` → `hci_powered_update_sync` → `hci_powered_update_adv_sync`). 2. **Small and Contained**: The fix is a single character change (|| to &&) that only affects the conditional logic. No architectural changes or new features are introduced. 3. **Prevents Resource Waste**: The bug causes unnecessary advertising instance creation on every Bluetooth startup, which wastes system resources and may interfere with user-configured advertising settings. 4. **Low Risk**: The change is minimal and only affects the specific condition for creating default advertising. The same pattern (checking both flags with AND) is already used in other parts of the codebase (e.g., `reenable_adv_sync()` function). 5. **User-Visible Impact**: The issue has an associated BlueZ bug report (#1442), indicating real users are affected by this problem. 6. **Long-Standing Issue**: The problematic code was introduced in commit cf75ad8b41d2a (October 2021), meaning this bug has been affecting users for an extended period across multiple kernel versions. The fix follows stable kernel rules perfectly: it's a important bugfix with minimal code change and very low regression risk, making it an ideal candidate for stable backporting. net/bluetooth/hci_sync.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c index 7938c004071c..795952d5f921 100644 --- a/net/bluetooth/hci_sync.c +++ b/net/bluetooth/hci_sync.c @@ -3344,7 +3344,7 @@ static int hci_powered_update_adv_sync(struct hci_dev *hdev) * advertising data. This also applies to the case * where BR/EDR was toggled during the AUTO_OFF phase. */ - if (hci_dev_test_flag(hdev, HCI_ADVERTISING) || + if (hci_dev_test_flag(hdev, HCI_ADVERTISING) && list_empty(&hdev->adv_instances)) { if (ext_adv_capable(hdev)) { err = hci_setup_ext_adv_instance_sync(hdev, 0x00); -- 2.50.1
