Re: [PATCH 2/2] ath10k: switch to ieee80211_tx_dequeue_ni

From: Erik Stromdahl
Date: Wed Oct 09 2019 - 15:23:36 EST

On 10/1/19 7:13 PM, Peter Oh wrote:

On 10/1/19 4:48 AM, Kalle Valo wrote:
Erik Stromdahl <erik.stromdahl@xxxxxxxxx> 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@xxxxxxxxx>
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

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.

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.