linux-kernel - Re: [Regression] rt2800usb - Wifi performance issues and connection drops

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <42185fa2-4191-fcf5-9c0f-fd7098bb856b@nbd.name>
Date:   Wed, 8 Mar 2023 12:57:26 +0100
From:   Felix Fietkau <nbd@....name>
To:     Alexander Wetzel <alexander@...zel-home.de>,
        Linux regressions mailing list <regressions@...ts.linux.dev>
Cc:     "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Mann <rauchwolke@....net>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Helmut Schaa <helmut.schaa@...glemail.com>,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [Regression] rt2800usb - Wifi performance issues and connection
 drops

On 08.03.23 12:41, Alexander Wetzel wrote:
> On 08.03.23 08:52, Felix Fietkau wrote:
> 
>>> I'm also planning to provide some more debug patches, to figuring out
>>> which part of commit 4444bc2116ae ("wifi: mac80211: Proper mark iTXQs
>>> for resumption") fixes the issue for you. Assuming my understanding
>>> above is correct the patch should not really fix/break anything for
>>> you...With the findings above I would have expected your git bisec to
>>> identify commit a790cc3a4fad ("wifi: mac80211: add wake_tx_queue
>>> callback to drivers") as the first broken commit...
>> I can't point to any specific series of events where it would go wrong, 
>> but I suspect that the problem might be the fact that you're doing tx 
>> scheduling from within ieee80211_handle_wake_tx_queue. I don't see how 
>> it's properly protected from potentially being called on different CPUs 
>> concurrently.
>> 
>> Back when I was debugging some iTXQ issues in mt76, I also had problems 
>> when tx scheduling could happen from multiple places. My solution was to 
>> have a single worker thread that handles tx, which is scheduled from the 
>> wake_tx_queue op.
>> Maybe you could do something similar in mac80211 for non-iTXQ drivers.
>> 
> 
> I think it's already doing all of that:
> ieee80211_handle_wake_tx_queue() is the mac80211 implementation for the
> wake_tx_queue op. The drivers without native iTXQ support simply link it
> to this handler.
I know. The problem I see is that I can't find anything that guarantees 
that .wake_tx_queue_op is not being called concurrently from multiple 
different places. ieee80211_handle_wake_tx_queue is doing the scheduling 
directly, instead of deferring it to a single workqueue/tasklet/thread, 
and multiple concurrent calls to it could potentially cause issues.

- Felix