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



On 11/11/2014 04:20 PM, Daniel P. Berrange wrote:
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


Thanks for the review, I've sent a v2 to address some code order issues
pointed out by John.

Pavel


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