Re: [PATCH v3 1/1] wifi: mac80211: fortify the spinlock against deadlock by interrupt

[Mirsad Goran Todorovac]

On 25.4.2023. 17:33, Leon Romanovsky wrote:
> On Tue, Apr 25, 2023 at 11:35:48AM +0200, Mirsad Goran Todorovac wrote:
> > In the function ieee80211_tx_dequeue() there is a particular 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 will cause a costly reset of the CPU and the wifi device or an
> > altogether hang in the single CPU and single core scenario.
> >
> > This is the probable trace 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 ***
>
> Can you please add to the commit message whole lockdep trace?
>
> And please trim "Apr 10 00:58:33 marvin-IdeaPad-3-15ITL6 kernel: " line prefix,
> it doesn't add any value.

Sure. I will do this ASAP. I thought of it myself, but I reckoned it would
be an overkill.

Will come in PATCH v4.

Best regards,
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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