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Message-ID: <CAB_54W4A6-Jgpr2WX3y3OPo-3=BJJDz+M5XPfWwpgCx1sXWAGQ@mail.gmail.com>
Date: Sun, 13 Mar 2022 16:43:52 -0400
From: Alexander Aring <alex.aring@...il.com>
To: Miquel Raynal <miquel.raynal@...tlin.com>
Cc: Stefan Schmidt <stefan@...enfreihafen.org>,
linux-wpan - ML <linux-wpan@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
David Girault <david.girault@...vo.com>,
Romuald Despres <romuald.despres@...vo.com>,
Frederic Blain <frederic.blain@...vo.com>,
Nicolas Schodet <nico@...fr.eu.org>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next v2 13/14] net: mac802154: Introduce a tx queue
flushing mechanism
Hi,
On Fri, Mar 4, 2022 at 5:54 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> I had a second look at it and it appears to me that the issue was
> already there and is structural. We just did not really cared about it
> because we didn't bother with synchronization issues.
>
I am not sure if I understand correctly. We stop the queue at some
specific moment and we need to make sure that xmit_do() is not called
or can't be called anymore.
I was thinking about:
void ieee802154_disable_queue(struct ieee802154_hw *hw)
{
struct ieee802154_local *local = hw_to_local(hw);
struct ieee802154_sub_if_data *sdata;
rcu_read_lock();
list_for_each_entry_rcu(sdata, &local->interfaces, list) {
if (!sdata->dev)
continue;
netif_tx_disable(sdata->dev);
}
rcu_read_unlock();
}
EXPORT_SYMBOL(ieee802154_stop_queue);
>From my quick view is that "netif_tx_disable()" ensures by holding
locks and other things and doing netif_tx_stop_queue() it we can be
sure there will be no xmit_do() going on while it's called and
afterwards. It can be that there are still transmissions on the
transceiver that are on the way, but then your atomic counter and
wait_event() will come in place.
We need to be sure there will be nothing queued anymore for
transmission what (in my opinion) tx_disable() does. from any context.
We might need to review some netif callbacks... I have in my mind for
example stop(), maybe netif_tx_stop_queue() is enough (because the
context is like netif_tx_disable(), helding similar locks, etc.) but
we might want to be sure that nothing is going on anymore by using
your wait_event() with counter.
Is there any problem which I don't see?
- Alex
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