[PATCH 0/2] Bluetooth: fix a permanent LE Set Advertising Parameters retry loop after a cancelled central connection

[PATCH 0/2] Bluetooth: fix a permanent LE Set Advertising Parameters retry loop after a cancelled central connection

[Valentin Kindschi]

A gateway device that advertises as a peripheral while also making
outgoing central connections gets stuck logging

	Bluetooth: hci0: Opcode 0x2006 failed: -16

every 2 s indefinitely, starting seconds after an outgoing connection
attempt times out and is cancelled. Measured on one unit: 5326
occurrences over 3 hours, ending only when bluetoothd was restarted,
which resets the controller.

The controller is behaving per specification: LE Set Advertising
Parameters is Command Disallowed while advertising is enabled. The host
issues it anyway, and then cannot recover.

Sequence, from btmon (BCM43455, no LE Extended Advertising, so legacy
advertising and the software rotation loop are in use):

  LE Create Connection                     Status Success
  ... 13.8 s, peer does not answer ...
  LE Set Advertising Parameters   0x2006    Success        \ done: resume
  LE Set Advertising Enable       0x200a    Success        / HCI_LE_ADV set
  LE Create Connection Cancel     0x200e    Success
  LE Connection Complete                    Unknown Conn Id
  LE Set Advertising Parameters   0x2006    Command Disallowed   [+63 ms]
  LE Set Advertising Parameters   0x2006    Command Disallowed   [+1.954 s]
  LE Set Advertising Parameters   0x2006    Command Disallowed   [+2.016 s]
  ... every ~2.016 s, for hours, and no 0x200a is ever sent again

Three connection attempts earlier in the same capture that *succeeded*
show the same 0x2006 + 0x200a pair and do not trigger this. Only an
attempt that times out and is cancelled does.

Why it never recovers: hci_enable_advertising_sync() returns as soon as
LE Set Advertising Parameters fails, before the LE Set Advertising Enable
that would set HCI_LE_ADV. hci_schedule_adv_instance_sync() re-arms
adv_instance_expire every HCI_DEFAULT_ADV_DURATION (2 s) and its
"already advertising" shortcut tests HCI_LE_ADV, which can no longer
become true. hci_disable_advertising_sync() cannot break the tie either -
it returns without sending anything while HCI_LE_ADV is clear, which is
exactly when the flag is wrong.

Patch 1 removes the redundant advertising enable that creates the
mismatch. Patch 2 stops HCI_LE_ADV being cleared for a connection
complete that reports no connection.

Patch 1 has been verified on the affected device. btmon counts:

  before, 2.6 min capture: 78 LE Set Advertising Parameters sent,
                           78 Command Disallowed, 0 LE Set Advertising
                           Enable sent
  after,  2.0 min capture:  3 LE Set Advertising Parameters sent,
                            0 Command Disallowed, 5 LE Set Advertising
                            Enable sent, all successful

The enable being sent and accepted again is the point: HCI_LE_ADV gets
set, so the rotation loop's shortcut works and nothing accumulates.

Patch 2 was deployed together with patch 1, so its effect is not
separately attributable on hardware; it is included because the same
mismatch is reachable through le_conn_complete_evt() independently, and
the current unconditional clear is wrong on its own terms.

Both apply to bluetooth-next and, unchanged, to 6.12.y - the affected
code is identical in both.

A third, unrelated Command Disallowed on the same device - LE Set Random
Address refused on every active scan restart because advertising is only
paused for the address update when LL privacy is in use - is sent
separately, as it has a different cause and touches hci_sync.c only.

Tooling disclosure (Documentation/process/generated-content.rst):
the bug was found and the patches drafted with the help of an AI coding
assistant, over a debugging session on the affected hardware. The inputs
were btmon captures and kernel logs from the device; the assistant was
asked to identify what re-issues LE Set Advertising Parameters every 2 s
and to propose a fix. Its first two proposed mechanisms were wrong and
were discarded after being checked against the captures; a third proposed
change (making hci_disable_advertising_sync() always emit the disable)
was built and tested on the device, broke advertising registration
outright, and was dropped. The two patches here are what survived. All
code and reasoning were reviewed by the submitter, and the verification
numbers above were measured on hardware.

Valentin Kindschi (2):
  Bluetooth: hci_conn: only re-enable advertising after a failed
    peripheral connection
  Bluetooth: hci_event: keep HCI_LE_ADV set when the host cancelled the
    connection

 net/bluetooth/hci_conn.c  |  3 ++-
 net/bluetooth/hci_event.c |  8 +++++---
 2 files changed, 7 insertions(+), 4 deletions(-)

--
2.34.1

[PATCH 1/2] Bluetooth: hci_conn: only re-enable advertising after a failed peripheral connection

[Valentin Kindschi]

hci_le_conn_failed() unconditionally calls hci_enable_advertising(),
although its own comment states advertising should be re-enabled only
when the failed attempt was made as a peripheral.

hci_le_conn_failed() is reached from hci_conn_failed() for every failed
LE connection, including outgoing central connections. For a central
attempt this enable is redundant: hci_le_create_conn_sync() already
restores advertising via hci_resume_advertising_sync() in its done:
block. Because hci_enable_advertising() only queues the work on
cmd_sync_work, it runs *after* that resume has already succeeded and
set HCI_LE_ADV.

The resulting HCI sequence, captured on a BCM43455 (no LE Extended
Advertising, so legacy advertising is used):

  LE Create Connection                     Status Success
  ... 13.8 s, peer never answers ...
  LE Set Advertising Parameters (0x2006)   Success   <- done: resume,
  LE Set Advertising Enable     (0x200a)   Success      HCI_LE_ADV set
  LE Create Connection Cancel   (0x200e)   Success
  LE Connection Complete                   Unknown Conn Id
  LE Set Advertising Parameters (0x2006)   Command Disallowed (0x0c)

The last command is the queued enable from hci_le_conn_failed() running
as a second hci_enable_advertising_sync() pass. It clears HCI_LE_ADV
(hci_sync.c, "Clear the HCI_LE_ADV bit temporarily"), then sends
LE Set Advertising Parameters while the controller is still advertising,
which the controller correctly rejects with Command Disallowed.

The disable-first call at the top of hci_enable_advertising_sync()
cannot prevent this: hci_disable_advertising_sync() returns early
without sending anything when HCI_LE_ADV is clear, so it is a no-op
exactly when the flag is wrong.

hci_enable_advertising_sync() then returns without sending LE Set
Advertising Enable, so HCI_LE_ADV is never set again. The legacy
software rotation loop re-arms hci_schedule_adv_instance_sync() every
HCI_DEFAULT_ADV_DURATION (2 s), and its "already advertising" shortcut
tests HCI_LE_ADV, which can no longer become true. The command is
therefore retried every 2 s indefinitely:

  Bluetooth: hci0: Opcode 0x2006 failed: -16

Observed on a gateway as 5326 occurrences over 3 hours, ending only when
bluetoothd was restarted. Connection attempts that succeed do not call
hci_le_conn_failed() and never trigger this.

Add the role test the comment already describes. Both other
hci_enable_advertising() call sites reached from a failed/closed LE
connection (hci_cs_disconnect() and hci_disconn_complete_evt()) already
guard on conn->role == HCI_ROLE_SLAVE; this one was missed.

Reproducing needs legacy advertising (ext_adv_capable() false, so the
software rotation loop is used), simultaneous peripheral advertising and
outgoing central connects, and a central connect that times out rather
than failing fast.

The Fixes tag points at the commit that introduced the advertising
restart into this path for the directed-advertising (peripheral) case;
the role test that the later commit 0b1db38ca26b ("Bluetooth: Fix check
for direct advertising") added to the sibling paths was never applied
here.

Fixes: 3c857757ef6e ("Bluetooth: Add directed advertising support through connect()")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5 btmon
Signed-off-by: Valentin Kindschi <valentin.kindschi@fiveco.ch>
---
 net/bluetooth/hci_conn.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1262,7 +1262,8 @@ static void hci_le_conn_failed(struct hci_conn *conn, u8 status)
 	/* Enable advertising in case this was a failed connection
 	 * attempt as a peripheral.
 	 */
-	hci_enable_advertising(hdev);
+	if (conn->role == HCI_ROLE_SLAVE)
+		hci_enable_advertising(hdev);
 }

 /* This function requires the caller holds hdev->lock */
--
2.34.1

[PATCH 2/2] Bluetooth: hci_event: keep HCI_LE_ADV set when the host cancelled the connection

[Valentin Kindschi]

le_conn_complete_evt() clears HCI_LE_ADV before looking at the event
status:

	/* All controllers implicitly stop advertising in the event of a
	 * connection, so ensure that the state bit is cleared.
	 */
	hci_dev_clear_flag(hdev, HCI_LE_ADV);

The premise fails for Unknown Connection Identifier (0x02), which is
what an HCI_LE_Connection_Complete carries after the host issued
LE Create Connection Cancel: no connection was created and the
controller never stopped advertising. Clearing the flag there makes the
host believe advertising is off while the controller has it on.

Other non-zero statuses must keep clearing it. Advertising Timeout
(0x3c) in particular means the controller gave up advertising on its
own, so the flag has to go; leaving it set would make the
"already advertising" shortcut in hci_schedule_adv_instance_sync() skip
the HCI commands and silently stop advertising altogether.

With legacy advertising the disagreement is self-sustaining. On the next
software rotation tick hci_enable_advertising_sync() runs:

  - hci_disable_advertising_sync() returns early without sending
    anything, because HCI_LE_ADV is clear;
  - LE Set Advertising Parameters is then sent while the controller is
    still advertising, and is correctly rejected with Command Disallowed
    (0x0c);
  - the function returns before LE Set Advertising Enable, so nothing
    re-sets HCI_LE_ADV.

hci_schedule_adv_instance_sync() re-arms adv_instance_expire every
HCI_DEFAULT_ADV_DURATION (2 s) and its "already advertising" shortcut
tests HCI_LE_ADV, which can no longer become true, so the command is
retried every 2 s indefinitely:

  Bluetooth: hci0: Opcode 0x2006 failed: -16

Captured on a BCM43455 (no LE Extended Advertising) after a central
connection attempt timed out and was cancelled:

  LE Set Advertising Parameters (0x2006)   Success
  LE Set Advertising Enable     (0x200a)   Success        HCI_LE_ADV set
  LE Create Connection Cancel   (0x200e)   Success
  LE Connection Complete                   Unknown Conn Id  <- flag cleared
  LE Set Advertising Parameters (0x2006)   Command Disallowed  [+2.033 s]
  LE Set Advertising Parameters (0x2006)   Command Disallowed  [+2.016 s]
  ...

Keep the flag only for the host-cancelled case.

Fixes: fbd96c151cdc ("Bluetooth: Fix clearing HCI_LE_ADV for LE connections")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5 btmon
Signed-off-by: Valentin Kindschi <valentin.kindschi@fiveco.ch>
---
 net/bluetooth/hci_event.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -5646,10 +5646,12 @@ static void le_conn_complete_evt(struct hci_dev *hdev, u8 status,

 	hci_dev_lock(hdev);

-	/* All controllers implicitly stop advertising in the event of a
-	 * connection, so ensure that the state bit is cleared.
+	/* Advertising stops when a connection is created, and when the
+	 * controller gives up advertising on its own. It keeps advertising
+	 * when the host cancelled an outgoing connection.
 	 */
-	hci_dev_clear_flag(hdev, HCI_LE_ADV);
+	if (status != HCI_ERROR_UNKNOWN_CONN_ID)
+		hci_dev_clear_flag(hdev, HCI_LE_ADV);

 	/* Check for existing connection:
 	 *
--
2.34.1

RE: Bluetooth: fix a permanent LE Set Advertising Parameters retry loop after a cancelled central connection

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 553 bytes --]

This is an automated email and please do not reply to this email.

Dear Submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
While preparing the CI tests, the patches you submitted couldn't be applied to the current HEAD of the repository.

----- Output -----

error: patch failed: net/bluetooth/hci_event.c:5646
error: net/bluetooth/hci_event.c: patch does not apply
hint: Use 'git am --show-current-patch' to see the failed patch

Please resolve the issue and submit the patches again.


---
Regards,
Linux Bluetooth

RE: Bluetooth: fix a permanent LE Set Advertising Parameters retry loop after a cancelled central connection

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 3280 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1147230

---Test result---

Test Summary:
CheckPatch                    PASS      1.11 seconds
VerifyFixes                   PASS      0.08 seconds
VerifySignedoff               PASS      0.08 seconds
GitLint                       FAIL      0.42 seconds
SubjectPrefix                 PASS      0.14 seconds
BuildKernel                   PASS      30.86 seconds
CheckAllWarning               PASS      29.99 seconds
CheckSparse                   PASS      28.66 seconds
BuildKernel32                 PASS      26.43 seconds
CheckKernelLLVM               SKIP      0.00 seconds
TestRunnerSetup               PASS      504.11 seconds
TestRunner_l2cap-tester       PASS      66.41 seconds
TestRunner_iso-tester         PASS      92.33 seconds
TestRunner_bnep-tester        PASS      20.05 seconds
TestRunner_mgmt-tester        FAIL      227.27 seconds
TestRunner_rfcomm-tester      PASS      26.15 seconds
TestRunner_sco-tester         PASS      35.67 seconds
TestRunner_ioctl-tester       PASS      27.18 seconds
TestRunner_mesh-tester        FAIL      26.36 seconds
TestRunner_smp-tester         PASS      24.43 seconds
TestRunner_userchan-tester    PASS      20.67 seconds
TestRunner_6lowpan-tester     PASS      24.35 seconds
IncrementalBuild              PASS      28.77 seconds

Details
##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
[v2,1/2] Bluetooth: hci_conn: only re-enable advertising after a failed peripheral connection

1: T1 Title exceeds max length (93>80): "[v2,1/2] Bluetooth: hci_conn: only re-enable advertising after a failed peripheral connection"
[v2,2/2] Bluetooth: hci_event: keep HCI_LE_ADV set when the host cancelled the connection

1: T1 Title exceeds max length (89>80): "[v2,2/2] Bluetooth: hci_event: keep HCI_LE_ADV set when the host cancelled the connection"
6: B3 Line contains hard tab characters (\t): "	/* All controllers implicitly stop advertising in the event of a"
7: B3 Line contains hard tab characters (\t): "	 * connection, so ensure that the state bit is cleared."
8: B3 Line contains hard tab characters (\t): "	 */"
9: B3 Line contains hard tab characters (\t): "	hci_dev_clear_flag(hdev, HCI_LE_ADV);"
##############################
Test: CheckKernelLLVM - SKIP
Desc: Build kernel with LLVM + context analysis
Output:
Clang not found
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 501, Passed: 496 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.256 seconds
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    2.508 seconds
Mesh - Send cancel - 2                               Timed out    1.984 seconds


https://github.com/bluez/bluetooth-next/pull/599

---
Regards,
Linux Bluetooth