Subject: Re: [PATCH] mac80211: do not call driver wake_tx_queue op during
 reconfig
To:     Ben Greear <greearb@candelatech.com>,
        linux-wireless@vger.kernel.org
Cc:     johannes@sipsolutions.net, stable@vger.kernel.org
References: <20190301134837.88087-1-nbd@nbd.name>
 <09a12ed0-dd86-2077-9ecb-c62a52186952@candelatech.com>
From:   Felix Fietkau <nbd@nbd.name>
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Message-ID: <c39a8e18-4a6b-a4db-3b25-c7d9d417d247@nbd.name>
Date:   Fri, 1 Mar 2019 17:06:48 +0100
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On 2019-03-01 16:29, Ben Greear wrote:
> On 3/1/19 5:48 AM, Felix Fietkau wrote:
>> There are several scenarios in which mac80211 can call drv_wake_tx_queue
>> after ieee80211_restart_hw has been called and has not yet completed.
>> Driver private structs are considered uninitialized until mac80211 has
>> uploaded the vifs, stations and keys again, so using private tx queue
>> data during that time is not safe.
>> 
>> The driver can also not rely on drv_reconfig_complete to figure out when
>> it is safe to accept drv_wake_tx_queue calls again, because it is only
>> called after all tx queues are woken again.
>> 
>> To fix this, bail out early in drv_wake_tx_queue if local->in_reconfig
>> is set.
> 
> This reminded me of a patch I posted back in 2016.  The discussion just sort of
> ended on it, but curious if you have a new opinion on it after debugging the
> issue in this patch:
> 
> https://patchwork.kernel.org/patch/9457709/
> 
> For what its worth, I've been using the patch above since I posted it, and
> it seems to work well for ath9k and ath10k.
I agree with what Johannes wrote about that patch. Fixing this could
likely be as simple as clearing IEEE80211_SDATA_IN_DRIVER on all
interfaces before bringing any of them back up. That way the normal
interface add logic applies without nasty special cases.
The reconfig code checks for ieee80211_sdata_running (which is
unaffected), so I don't think we need to save the previous value of that
flag.

- Felix