From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Luca Coelho <luca@coelho.fi>, johannes@sipsolutions.net
Cc:     luca@coelho.fi, linux-wireless@vger.kernel.org
Subject: Re: [PATCH 15/16] mac80211: agg-tx: don't schedule_and_wake_txq()
 under sta->lock
In-Reply-To: <iwlwifi.20211129152938.d5fceeb7e166.I555fef8e67d93fff3d9a304886c4a9f8b322e591@changeid>
References: <20211129133248.83829-1-luca@coelho.fi>
 <iwlwifi.20211129152938.d5fceeb7e166.I555fef8e67d93fff3d9a304886c4a9f8b322e591@changeid>
Date:   Mon, 29 Nov 2021 14:54:31 +0100
Message-ID: <8735nf9ieg.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Luca Coelho <luca@coelho.fi> writes:

> From: Johannes Berg <johannes.berg@intel.com>
>
> When we call ieee80211_agg_start_txq(), that will in turn call
> schedule_and_wake_txq(). Called from ieee80211_stop_tx_ba_cb()
> this is done under sta->lock, which leads to certain circular
> lock dependencies, as reported by Chris Murphy:
> https://lore.kernel.org/r/CAJCQCtSXJ5qA4bqSPY=oLRMbv-irihVvP7A2uGutEbXQVkoNaw@mail.gmail.com
>
> In general, ieee80211_agg_start_txq() is usually not called
> with sta->lock held, only in this one place. But it's always
> called with sta->ampdu_mlme.mtx held, and that's therefore
> clearly sufficient.
>
> Change ieee80211_stop_tx_ba_cb() to also call it without the
> sta->lock held, by factoring it out of ieee80211_remove_tid_tx()
> (which is only called in this one place).
>
> This breaks the locking chain and makes it less likely that
> we'll have similar locking chain problems in the future.
>
> Reported-by: Chris Murphy <lists@colorremedies.com>
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

Does this need a fixes: tag?

-Toke