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

[Leon Romanovsky]

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.

Thanks