[libvirt] [PATCH] nwfilter: fix deadlock caused updating network device and nwfilter

[Daniel P. Berrange]

On Wed, Nov 05, 2014 at 03:02:03PM +0100, Pavel Hrdina wrote:
> Commit 6e5c79a1 tried to fix deadlock between nwfilter{Define,Undefine}
> and starting of guest, but this same deadlock is also for
> updating/attaching network device to domain.
> 
> The deadlock was introduced by removing global QEMU driver lock because
> nwfilter was counting on this lock and ensure that all driver locks are
> locked inside of nwfilter{Define,Undefine}.
> 
> This patch extends usage of virNWFilterReadLockFilterUpdates to prevent
> the deadlock for all possible paths in QEMU driver. LXC and UML drivers
> still have global lock.

ACK, conceptually it makes sense that we need to hold the read lock
in these methods. Concurrency should still be good because it is
only a read lock, not a write lock.

Regards,
Daniel
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