Host cherry pick tx processor thread #3606
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ATT is invoking user callbacks in its net_buf destroy function. It is
common practice that these callbacks can block on bt_hci_cmd_alloc().
This is a deadlock when the net_buf_unref() happens inside the HCI
driver, invoked from tx_processor.
Blocking callbacks like this appear in our own samples. See further down
about how this problem was detected.
tx_processor not protect against blocking callbacks so it is de-facto
forbidden. The Host should not equip net_bufs with dangerous destroy
callbacks.
This commit makes ATT defer its net_buf destruction and user callback
invocation to the system workqueue, so that net_buf_unref is safe to
call from non-blocking threads. In the case of the deadlock, the
net_buf_unref() was below the tx_processor in the call stack, which (at
the time of this commit) is on the system work queue, so defering it to
the system work queue is preserving the existing behavior.
Future improvement may be to allow the user to provide their own
workqueue for ATT callbacks.
This deadlock was detected because the following test was failing while
moving tx_processor to the bt_taskq:
tests/bsim/bluetooth/ll/throughput/tests_scripts/gatt_write.sh
The above test has an ATT callback `write_cmd_cb` invokes
`bt_conn_le_param_update` can block waiting for `tx_processor`.
The reason it was not failing while tx_processor was on the system work
queue is that the GATT API has a special non-blocking behavior when
called from the system work queue.
Signed-off-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no>
(cherry picked from commit 6889042)
Signed-off-by: Kyra Lengfeld <kyra.lengfeld@nordicsemi.no>
…al_identity Reduce BT_MAX_CONN from 62 to 61 to make it build on integration platform qemu_cortex_m3/ti_lm3s6965 when we add bt_taskq in subsequent commit. The number 62 seems arbitrary here, so reducing it by one should not have any practical impact. Signed-off-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no> (cherry picked from commit 0ee5d70) Signed-off-by: Kyra Lengfeld <kyra.lengfeld@nordicsemi.no>
When thread that TX processor is used to send commands and data to Controller is also used for sync commands sending and command buffer allocation, a deadlock happens. This thread is used to avoid such deadlocks by moving TX processor to its own dedicated thread exclusively used by tx processor only. Co-authored-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no> Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no> Signed-off-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no> (cherry picked from commit f101976) Signed-off-by: Kyra Lengfeld <kyra.lengfeld@nordicsemi.no>
The workaround in bt_cmd_send_sync should no longer by needed when tx_processor is not on the system work queue. Signed-off-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no> (cherry picked from commit 04b8dba) Signed-off-by: Kyra Lengfeld <kyra.lengfeld@nordicsemi.no>
NordicBuilder
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Automatically created by action-manifest-pr GH action from PR: nrfconnect/sdk-zephyr#3606 Signed-off-by: Nordic Builder <pylon@nordicsemi.no>
KyraLengfeld
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to NordicBuilder/sdk-nrf
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Dec 5, 2025
Automatically created by action-manifest-pr GH action from PR: nrfconnect/sdk-zephyr#3606 Signed-off-by: Nordic Builder <pylon@nordicsemi.no>
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Cherry picks the four commits from zephyrproject-rtos/zephyr#97913 to run tx_processor on its own thread.