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Message-ID: <cdc80531-f25f-6f9d-b15f-25e16130b53a@alu.unizg.hr>
Date:   Tue, 25 Apr 2023 10:29:35 +0200
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Subject: Re: [PATCH RFC v1 1/1] net: mac80211: fortify the spinlock against
 deadlock in interrupt
To:     Johannes Berg <johannes@sipsolutions.net>,
        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>
References: <20230423082403.49143-1-mirsad.todorovac@alu.unizg.hr>
 <017c5178594e2df6ca02f2d7ffa9109755315c56.camel@sipsolutions.net>
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From:   Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
In-Reply-To: <017c5178594e2df6ca02f2d7ffa9109755315c56.camel@sipsolutions.net>
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On 24.4.2023. 19:27, Johannes Berg wrote:
> On Sun, 2023-04-23 at 10:24 +0200, Mirsad Goran Todorovac wrote:
>> In the function ieee80211_tx_dequeue() there is a locking sequence:
>>
>> begin:
>> 	spin_lock(&local->queue_stop_reason_lock);
>> 	q_stopped = local->queue_stop_reasons[q];
>> 	spin_unlock(&local->queue_stop_reason_lock);
>>
>> 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.
>>
>> This is the only remaining spin_lock() on local->queue_stop_reason_lock
>> that did not disable interrupts and could have possibly caused the deadlock
>> on the same CPU (core).
>>
>> This will cause a costly reset of the CPU and wifi device or an
>> altogether hang in the single CPU and single core scenario.
>>
>> This is the probable reproduce of the deadlock:
>>
>> 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_stop_reason_lock);
>> Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel:
>>                                                   *** DEADLOCK ***
>>
>> 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

Will do, Sir. Do I have an Acked-by: ?

Thank you.

Mirsad

-- 
Mirsad Todorovac
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb
Republic of Croatia, the European Union

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