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SubjectRe: [PATCH 2/2] ath10k: switch to ieee80211_tx_dequeue_ni
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On 10/9/19 9:23 PM, Erik Stromdahl wrote:
>
>
> On 10/1/19 7:13 PM, Peter Oh wrote:
>>
>> On 10/1/19 4:48 AM, Kalle Valo wrote:
>>> Erik Stromdahl <erik.stromdahl@gmail.com> writes:
>>>
>>>> Since ath10k_mac_tx_push_txq() can be called from process context, we
>>>> must explicitly disable softirqs before the call into mac80211.
>>>>
>>>> By calling ieee80211_tx_dequeue_ni() instead of ieee80211_tx_dequeue()
>>>> we make sure softirqs are always disabled even in the case when
>>>> ath10k_mac_tx_push_txq() is called from process context.
>>>>
>>>> Calling ieee80211_tx_dequeue_ni() with softirq's already disabled
>>>> (e.g., from softirq context) should be safe as the local_bh_disable()
>>>> and local_bh_enable() functions (called from ieee80211_tx_dequeue_ni)
>>>> are fully reentrant.
>>>>
>>>> Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
>>> I already applied this, but I still want to check _why_ you are changing
>>> this? Is it that you want to call ath10k_mac_tx_push_pending() from a
>>> workqueue in sdio.c in a future patch, or what? Because at the moment me
>>> and Johannes were not able to find where this is called in process
>>> context.
>>>
> SDIO irqs are threaded irqs (at least on my iMX6 board) and hence process context.
> I will see if I can find a trace that shows the call chain more exactly.
>

I found this backtrace in a log file:
(it does not show the call to ieee80211_tx_dequeue_ni(), but it shows that
ath10k_sdio_irq_handler() is called from process context)

irq/62-mmc1-65 [000] .... 785.261081: ath10k_mac_op_wake_tx_queue <-ieee80211_queue_skb
irq/62-mmc1-65 [000] .... 785.261090: <stack trace>
=> ieee80211_queue_skb
=> __ieee80211_subif_start_xmit
=> ieee80211_subif_start_xmit
=> dev_hard_start_xmit
=> __dev_queue_xmit
=> dev_queue_xmit
=> ip_finish_output2
=> ip_finish_output
=> ip_output
=> ip_local_out
=> ip_queue_xmit
=> tcp_transmit_skb
=> tcp_write_xmit
=> __tcp_push_pending_frames
=> tcp_rcv_established
=> tcp_v4_do_rcv
=> tcp_v4_rcv
=> ip_local_deliver_finish
=> ip_local_deliver
=> ip_rcv_finish
=> ip_rcv
=> __netif_receive_skb_core
=> __netif_receive_skb
=> netif_receive_skb_internal
=> netif_receive_skb
=> ieee80211_deliver_skb
=> ieee80211_rx_handlers
=> ieee80211_prepare_and_rx_handle
=> ieee80211_rx_napi
=> ath10k_htt_t2h_msg_handler
=> ath10k_htt_htc_t2h_msg_handler
=> ath10k_sdio_mbox_rxmsg_pending_handler
=> ath10k_sdio_irq_handler <- ath10k_mac_tx_push_pending() is called from here
=> process_sdio_pending_irqs
=> sdio_run_irqs
=> sdhci_thread_irq
=> irq_thread_fn
=> irq_thread
=> kthread
=> ret_from_fork
=> 0

From ath10k_sdio_irq_handler(), the call chain down to ieee80211_tx_dequeue_ni()
looks like this:

ath10k_sdio_irq_handler() =>
ath10k_mac_tx_push_pending() =>
ath10k_mac_schedule_txq() =>
ath10k_mac_tx_push_txq() =>
ieee80211_tx_dequeue_ni()

>
>> It seems Johannes wants to fix it in mac80211.
>>
>> [PATCH v2] mac80211: keep BHs disabled while calling drv_tx_wake_queue()
>>
>> Drivers typically expect this, as it's the case for almost all cases
>> where this is called (i.e. from the TX path). Also, the code in mac80211
>> itself (if the driver calls ieee80211_tx_dequeue()) expects this as it
>> uses this_cpu_ptr() without additional protection.
>>

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