Re: [libvirt] [PATCH v3 2/2] virtlogd: add missing netserver refcount increment on reload
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)
>> virLockDaemonClientFree,
>> (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
concern.
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!
John
>
> Again- need to think a bit longer.
>
> John
>
>>
>> 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);
>>
>> virJSONValueFree(object);
>> virObjectUnlock(dmn);
>>