Re: [PATCH RFC v1 1/1] net: mac80211: fortify the spinlock against deadlock in interrupt

[Mirsad Goran Todorovac]

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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