Subject: Re: [PATCH] mac80211: do not call driver wake_tx_queue op during
 reconfig
From:   Felix Fietkau <nbd@nbd.name>
To:     Ben Greear <greearb@candelatech.com>,
        linux-wireless@vger.kernel.org
Cc:     johannes@sipsolutions.net
References: <20190301134837.88087-1-nbd@nbd.name>
 <09a12ed0-dd86-2077-9ecb-c62a52186952@candelatech.com>
 <c39a8e18-4a6b-a4db-3b25-c7d9d417d247@nbd.name>
Openpgp: preference=signencrypt
Autocrypt: addr=nbd@nbd.name; prefer-encrypt=mutual; keydata=
 mQGiBEah5CcRBADIY7pu4LIv3jBlyQ/2u87iIZGe6f0f8pyB4UjzfJNXhJb8JylYYRzIOSxh
 ExKsdLCnJqsG1PY1mqTtoG8sONpwsHr2oJ4itjcGHfn5NJSUGTbtbbxLro13tHkGFCoCr4Z5
 Pv+XRgiANSpYlIigiMbOkide6wbggQK32tC20QxUIwCg4k6dtV/4kwEeiOUfErq00TVqIiEE
 AKcUi4taOuh/PQWx/Ujjl/P1LfJXqLKRPa8PwD4j2yjoc9l+7LptSxJThL9KSu6gtXQjcoR2
 vCK0OeYJhgO4kYMI78h1TSaxmtImEAnjFPYJYVsxrhay92jisYc7z5R/76AaELfF6RCjjGeP
 wdalulG+erWju710Bif7E1yjYVWeA/9Wd1lsOmx6uwwYgNqoFtcAunDaMKi9xVQW18FsUusM
 TdRvTZLBpoUAy+MajAL+R73TwLq3LnKpIcCwftyQXK5pEDKq57OhxJVv1Q8XkA9Dn1SBOjNB
 l25vJDFAT9ntp9THeDD2fv15yk4EKpWhu4H00/YX8KkhFsrtUs69+vZQwbQcRmVsaXggRmll
 dGthdSA8bmJkQG5iZC5uYW1lPohgBBMRAgAgBQJGoeQnAhsjBgsJCAcDAgQVAggDBBYCAwEC
 HgECF4AACgkQ130UHQKnbvXsvgCgjsAIIOsY7xZ8VcSm7NABpi91yTMAniMMmH7FRenEAYMa
 VrwYTIThkTlQuQINBEah5FQQCACMIep/hTzgPZ9HbCTKm9xN4bZX0JjrqjFem1Nxf3MBM5vN
 CYGBn8F4sGIzPmLhl4xFeq3k5irVg/YvxSDbQN6NJv8o+tP6zsMeWX2JjtV0P4aDIN1pK2/w
 VxcicArw0VYdv2ZCarccFBgH2a6GjswqlCqVM3gNIMI8ikzenKcso8YErGGiKYeMEZLwHaxE
 Y7mTPuOTrWL8uWWRL5mVjhZEVvDez6em/OYvzBwbkhImrryF29e3Po2cfY2n7EKjjr3/141K
 DHBBdgXlPNfDwROnA5ugjjEBjwkwBQqPpDA7AYPvpHh5vLbZnVGu5CwG7NAsrb2isRmjYoqk
 wu++3117AAMFB/9S0Sj7qFFQcD4laADVsabTpNNpaV4wAgVTRHKV/kC9luItzwDnUcsZUPdQ
 f3MueRJ3jIHU0UmRBG3uQftqbZJj3ikhnfvyLmkCNe+/hXhPu9sGvXyi2D4vszICvc1KL4RD
 aLSrOsROx22eZ26KqcW4ny7+va2FnvjsZgI8h4sDmaLzKczVRIiLITiMpLFEU/VoSv0m1F4B
 FtRgoiyjFzigWG0MsTdAN6FJzGh4mWWGIlE7o5JraNhnTd+yTUIPtw3ym6l8P+gbvfoZida0
 TspgwBWLnXQvP5EDvlZnNaKa/3oBes6z0QdaSOwZCRA3QSLHBwtgUsrT6RxRSweLrcabiEkE
 GBECAAkFAkah5FQCGwwACgkQ130UHQKnbvW2GgCfTKx80VvCR/PvsUlrvdOLsIgeRGAAn1ee
 RjMaxwtSdaCKMw3j33ZbsWS4
Message-ID: <3bc506d5-8432-56d4-8588-afe7dea2eba3@nbd.name>
Date:   Fri, 1 Mar 2019 17:13:48 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0)
 Gecko/20100101 Thunderbird/60.5.1
MIME-Version: 1.0
In-Reply-To: <c39a8e18-4a6b-a4db-3b25-c7d9d417d247@nbd.name>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On 2019-03-01 17:06, Felix Fietkau wrote:
> 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.
How about this? (untested)
---
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1956,7 +1956,6 @@ static void ieee80211_flush_completed_scan(struct ieee80211_local *local,
 
 static void ieee80211_handle_reconfig_failure(struct ieee80211_local *local)
 {
-	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_chanctx *ctx;
 
 	/*
@@ -1980,9 +1979,6 @@ static void ieee80211_handle_reconfig_failure(struct ieee80211_local *local)
 	 */
 	ieee80211_sched_scan_end(local);
 
-	list_for_each_entry(sdata, &local->interfaces, list)
-		sdata->flags &= ~IEEE80211_SDATA_IN_DRIVER;
-
 	/* Mark channel contexts as not being in the driver any more to avoid
 	 * removing them from the driver during the shutdown process...
 	 */
@@ -2135,6 +2131,9 @@ int ieee80211_reconfig(struct ieee80211_local *local)
 
 	local->started = false;
 
+	list_for_each_entry(sdata, &local->interfaces, list)
+		sdata->flags &= ~IEEE80211_SDATA_IN_DRIVER;
+
 	/*
 	 * Upon resume hardware can sometimes be goofy due to
 	 * various platform / driver / bus issues, so restarting