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CA-96541/SCTX-1188: Fix race condition when creating metrics for VLAN…

… PIFs

This fixes a race condition between the thread that copies bonds and VLANs from
the master when a new slave joins the pool, and the thread that creates/updates
the PIF_metrics (the "monitor thread"). Or in fact a race between anything that
creates a bond and very soon after that a VLAN on top of it.

Since XCP1.6/XS6.1, VLANs no longer have their own PIF_metrics. Rather, they point
to the PIF_metrics of the underlying PIF, which can be either a physical PIF
(e.g. for eth0), or a bond PIF. Therefore, the carrier of a VLAN PIF is the same
as the carrier of the underlying PIF.

When a physical PIF or bond PIF is created, it does not immediately have
PIF_metrics (PIF.metrics = "OpaqueRef:NULL"). The PIF_metrics object is created
and assigned to the PIF by the monitor thread a short while after that. If you
create a VLAN before the PIF_metrics have been created, the PIF.metrics field from
the underlying PIF will still be copied, which is "OpaqueRef:NULL". This will never
get updated, because the monitor thread ignores VLANs.

The fix is simply to immediately create an (empty) metrics object when creating a

Signed-off-by: Rob Hoes <>
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1 parent 8ddb0a4 commit 140635d6855eda2c69785a49d84ce29a22eeb126 @robhoes committed Mar 15, 2013
Showing with 2 additions and 1 deletion.
  1. +2 −1 ocaml/xapi/
@@ -352,8 +352,9 @@ let create ~__context ~network ~members ~mAC ~mode ~properties =
(* Create master PIF and Bond objects *)
let device = choose_bond_device_name ~__context ~host in
let device_name = device in
+ let metrics = Xapi_pif.make_pif_metrics ~__context in
Db.PIF.create ~__context ~ref:master ~uuid:(Uuid.to_string (Uuid.make_uuid ()))
- ~device ~device_name ~network ~host ~mAC ~mTU:(-1L) ~vLAN:(-1L) ~metrics:Ref.null
+ ~device ~device_name ~network ~host ~mAC ~mTU:(-1L) ~vLAN:(-1L) ~metrics
~physical:false ~currently_attached:false
~ip_configuration_mode:`None ~iP:"" ~netmask:"" ~gateway:"" ~dNS:"" ~bond_slave_of:Ref.null
~vLAN_master_of:Ref.null ~management:false ~other_config:[] ~disallow_unplug:false

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