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

[Erik Stromdahl]

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
> > 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.


> 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.