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Message-ID: <017c5178594e2df6ca02f2d7ffa9109755315c56.camel@sipsolutions.net>
Subject: Re: [PATCH RFC v1 1/1] net: mac80211: fortify the spinlock against
 deadlock in interrupt
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Alexander Wetzel <alexander@wetzel-home.de>
Date:   Mon, 24 Apr 2023 19:27:08 +0200
In-Reply-To: <20230423082403.49143-1-mirsad.todorovac@alu.unizg.hr>
References: <20230423082403.49143-1-mirsad.todorovac@alu.unizg.hr>
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On Sun, 2023-04-23 at 10:24 +0200, Mirsad Goran Todorovac wrote:
> In the function ieee80211_tx_dequeue() there is a locking sequence:
>=20
> begin:
> 	spin_lock(&local->queue_stop_reason_lock);
> 	q_stopped =3D local->queue_stop_reasons[q];
> 	spin_unlock(&local->queue_stop_reason_lock);
>=20
> However small the chance (increased by ftracetest), an asynchronous
> interrupt can occur in between of spin_lock() and spin_unlock(),
> and the interrupt routine will attempt to lock the same
> &local->queue_stop_reason_lock again.
>=20
> This is the only remaining spin_lock() on local->queue_stop_reason_lock
> that did not disable interrupts and could have possibly caused the deadlo=
ck
> on the same CPU (core).
>=20
> This will cause a costly reset of the CPU and wifi device or an
> altogether hang in the single CPU and single core scenario.
>=20
> This is the probable reproduce of the deadlock:
>=20
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:  Possible unsafe locking =
scenario:
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:        CPU0
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:        ----
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:   lock(&local->queue_stop=
_reason_lock);
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:   <Interrupt>
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:     lock(&local->queue_st=
op_reason_lock);
> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:
>                                                  *** DEADLOCK ***
>=20
> Fixes: 4444bc2116ae

That fixes tag is wrong, should be

Fixes: 4444bc2116ae ("wifi: mac80211: Proper mark iTXQs for resumption")

Otherwise seems fine to me, submit it properly?

johannes