[libvirt] [PATCH v3 2/2] virtlogd: add missing netserver refcount increment on reload
jferlan at redhat.com
Wed Oct 25 09:48:52 UTC 2017
On 10/25/2017 05:15 AM, Nikolay Shirokovskiy wrote:
> On 25.10.2017 12:06, John Ferlan wrote:
>> On 10/24/2017 06:47 AM, Nikolay Shirokovskiy wrote:
>>> After virNetDaemonAddServerPostExec call in virtlogd we should have
>>> netserver refcount set to 2. One goes to netdaemon servers hashtable
>>> and one goes to virtlogd own reference to netserver. Let's add
>>> missing increment in virNetDaemonAddServerPostExec itself while holding
>>> daemon lock.
>>> We also have to unref new extra ref after virtlockd call to virNetDaemonAddServerPostExec.
>>> src/locking/lock_daemon.c | 1 +
>>> src/rpc/virnetdaemon.c | 1 +
>>> 2 files changed, 2 insertions(+)
>>> diff --git a/src/locking/lock_daemon.c b/src/locking/lock_daemon.c
>>> index fe3eaf9..41a06b2 100644
>>> --- a/src/locking/lock_daemon.c
>>> +++ b/src/locking/lock_daemon.c
>>> @@ -275,6 +275,7 @@ virLockDaemonNewPostExecRestart(virJSONValuePtr object, bool privileged)
>>> (void*)(intptr_t)(privileged ? 0x1 : 0x0))))
>>> goto error;
>>> + virObjectUnref(srv);
>> I need to think a bit more about this one... different model in lockd
>> vs. logd over @srv usage especially w/r/t this particular path.
>> I see that in this path eventually something calls virNetDaemonGetServer
>> instead of storing the @srv in order to add lockProgram... In any case,> I guess I'd be worried/concerned that something could remove @srv
>> causing the Hash table code to unref/delete the srv... Also, in the
>> cleanup: path of main() wouldn't the Unref(srv) cause problems?
> But this unref only balance newly added ref. If there are other
> problems with reference conting in virtlockd - its a different
Ok - so what I've learned is that virLockDaemonPostExecRestart returns
rv == 1 which indicates a successful restore resulting in a call to
virNetDaemonGetServer which will do a virObjectRef anyway leaving us
with (theoretically) 2 refs prior to the code that adds programs to @srv
(and less concern from my part of the subsequent Unref in cleanup: here).
If we saved srv in lockd like logd does, then we wouldn't need to call
virNetDaemonGetServer resulting in the same eventual result except for a
window after the Unref here where the refcnt == 1 until
virNetDaemonGetServer is run. Since I believe nothing could happen in
between that would cause the Unref due to HashFree being called, then I
think we're OK.
The concern being is if virNetDaemonGetServer didn't find the server,
then @srv would be NULL and the subsequent call to
virNetServerAddProgram for lockProgram would fail miserably, but I don't
think that can happen theoretically at least!
>> Again- need to think a bit longer.
>>> return lockd;
>>> diff --git a/src/rpc/virnetdaemon.c b/src/rpc/virnetdaemon.c
>>> index 495bc4b..f3e3ffe 100644
>>> --- a/src/rpc/virnetdaemon.c
>>> +++ b/src/rpc/virnetdaemon.c
>>> @@ -312,6 +312,7 @@ virNetDaemonAddServerPostExec(virNetDaemonPtr dmn,
>>> if (virHashAddEntry(dmn->servers, serverName, srv) < 0)
>>> goto error;
>>> + virObjectRef(srv);
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