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

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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

Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu




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