From: David Vrabel <david.vra...@citrix.com>
Date: Tue, 13 Jan 2015 16:42:42 +0000
> In netfront the Rx and Tx path are independent and use different
> locks. The Tx lock is held with hard irqs disabled, but Rx lock is
> held with only BH disabled. Since both sides use the same stats lock,
> a deadlock may occur.
>
> [ INFO: possible irq lock inversion dependency detected ]
> 3.16.2 #16 Not tainted
> ---------------------------------------------------------
> swapper/0/0 just changed the state of lock:
> (&(&queue->tx_lock)->rlock){-.....}, at: [<c03adec8>]
> xennet_tx_interrupt+0x14/0x34
> but this lock took another, HARDIRQ-unsafe lock in the past:
> (&stat->syncp.seq#2){+.-...}
> and interrupts could create inverse lock ordering between them.
> other info that might help us debug this:
> Possible interrupt unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&stat->syncp.seq#2);
> local_irq_disable();
> lock(&(&queue->tx_lock)->rlock);
> lock(&stat->syncp.seq#2);
> <Interrupt>
> lock(&(&queue->tx_lock)->rlock);
>
> Using separate locks for the Rx and Tx stats fixes this deadlock.
>
> Reported-by: Dmitry Piotrovsky <piotrovskydmi...@gmail.com>
> Signed-off-by: David Vrabel <david.vra...@citrix.com>
Applied, thanks.
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