From bbab997f4307da65856dedd3f319037ce442d17e Mon Sep 17 00:00:00 2001
Message-Id: <bbab997f4307da65856dedd3f319037ce442d17e@dist-git>
From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <berrange@redhat.com>
Date: Thu, 24 Feb 2022 18:41:29 +0000
Subject: [PATCH] nwfilter: hold filter update lock when creating/deleting
 bindings
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The nwfilter update lock is historically acquired by the virt
drivers in order to achieve serialization between nwfilter
define/undefine, and instantiation/teardown of filters.

When running in the modular daemons, however, the mutex that
the virt drivers are locking is in a completely different
process from the mutex that the nwfilter driver is locking.

Serialization is lost and thus call from the virt driver to
virNWFilterBindingCreateXML can deadlock with a concurrent
call to the virNWFilterDefineXML method.

The solution is surprisingly easy, the update lock simply
needs acquiring in the virNWFilterBindingCreateXML method
and virNWFilterBindingUndefine method instead of in the
virt drivers.

The only semantic difference here is that when a virtual
machine has multiple NICs, the instantiation and teardown
of filters is no longer serialized for the whole VM, but
rather for each NIC. This should not be a problem since
the virt drivers already need to cope with tearing down
a partially created VM where only some of the NICs are
setup.

Reviewed-by: Laine Stump <laine@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit 65dc79f50b96b34b2253601b8972d5ca90658f33)
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2044379
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/nwfilter/nwfilter_driver.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c
index 200451d6b1..a4479fc9fe 100644
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -760,12 +760,15 @@ nwfilterBindingCreateXML(virConnectPtr conn,
     if (!(ret = virGetNWFilterBinding(conn, def->portdevname, def->filter)))
         goto cleanup;
 
+    virNWFilterReadLockFilterUpdates();
     if (virNWFilterInstantiateFilter(driver, def) < 0) {
+        virNWFilterUnlockFilterUpdates();
         virNWFilterBindingObjListRemove(driver->bindings, obj);
         virObjectUnref(ret);
         ret = NULL;
         goto cleanup;
     }
+    virNWFilterUnlockFilterUpdates();
     virNWFilterBindingObjSave(obj, driver->bindingDir);
 
  cleanup:
@@ -802,7 +805,9 @@ nwfilterBindingDelete(virNWFilterBindingPtr binding)
     if (virNWFilterBindingDeleteEnsureACL(binding->conn, def) < 0)
         goto cleanup;
 
+    virNWFilterReadLockFilterUpdates();
     virNWFilterTeardownFilter(def);
+    virNWFilterUnlockFilterUpdates();
     virNWFilterBindingObjDelete(obj, driver->bindingDir);
     virNWFilterBindingObjListRemove(driver->bindings, obj);
 
-- 
2.35.1