On Tue, Jun 19, 2018 at 05:03 PM +0200, "Daniel P. Berrangé" <berrange@xxxxxxxxxx> wrote:
> On Tue, Jun 19, 2018 at 03:55:09PM +0100, Daniel P. Berrangé wrote:
>> On Tue, Jun 19, 2018 at 04:51:13PM +0200, Erik Skultety wrote:
>> > On Mon, Jun 18, 2018 at 12:38:06PM +0200, Marc Hartmayer wrote:
>> > > On Mon, Jun 18, 2018 at 09:47 AM +0200, Erik Skultety <eskultet@xxxxxxxxxx> wrote:
>> > > > On Fri, Jun 15, 2018 at 03:31:34PM +0200, Marc Hartmayer wrote:
>> > > >> On Fri, Jun 15, 2018 at 01:39 PM +0200, Marc Hartmayer <mhartmay@xxxxxxxxxxxxx> wrote:
>> > > >> > If srv->workers is a NULL pointer, as it is the case if there are no
>> > > >> > workers, then don't try to dereference it.
>> > > >> >
>> > > >> > Signed-off-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
>> > > >> > Reviewed-by: Boris Fiuczynski <fiuczy@xxxxxxxxxxxxx>
>> > > >> > ---
>> > > >> > src/rpc/virnetserver.c | 22 +++++++++++++++-------
>> > > >> > 1 file changed, 15 insertions(+), 7 deletions(-)
>> > > >> >
>> > > >> > diff --git a/src/rpc/virnetserver.c b/src/rpc/virnetserver.c
>> > > >> > index 5ae809e372..be6f610880 100644
>> > > >> > --- a/src/rpc/virnetserver.c
>> > > >> > +++ b/src/rpc/virnetserver.c
>> > > >> > @@ -933,13 +933,21 @@ virNetServerGetThreadPoolParameters(virNetServerPtr srv,
>> > > >> > size_t *jobQueueDepth)
>> > > >> > {
>> > > >> > virObjectLock(srv);
>> > > >> > -
>> > > >> > - *minWorkers = virThreadPoolGetMinWorkers(srv->workers);
>> > > >> > - *maxWorkers = virThreadPoolGetMaxWorkers(srv->workers);
>> > > >> > - *freeWorkers = virThreadPoolGetFreeWorkers(srv->workers);
>> > > >> > - *nWorkers = virThreadPoolGetCurrentWorkers(srv->workers);
>> > > >> > - *nPrioWorkers = virThreadPoolGetPriorityWorkers(srv->workers);
>> > > >> > - *jobQueueDepth = virThreadPoolGetJobQueueDepth(srv->workers);
>> > > >> > + if (srv->workers) {
>> > > >> > + *minWorkers = virThreadPoolGetMinWorkers(srv->workers);
>> > > >> > + *maxWorkers = virThreadPoolGetMaxWorkers(srv->workers);
>> > > >> > + *freeWorkers = virThreadPoolGetFreeWorkers(srv->workers);
>> > > >> > + *nWorkers = virThreadPoolGetCurrentWorkers(srv->workers);
>> > > >> > + *nPrioWorkers = virThreadPoolGetPriorityWorkers(srv->workers);
>> > > >> > + *jobQueueDepth = virThreadPoolGetJobQueueDepth(srv->workers);
>> > > >> > + } else {
>> > > >> > + *minWorkers = 0;
>> > > >> > + *maxWorkers = 0;
>> > > >> > + *freeWorkers = 0;
>> > > >> > + *nWorkers = 0;
>> > > >> > + *nPrioWorkers = 0;
>> > > >> > + *jobQueueDepth = 0;
>> > > >> > + }
>> > > >> >
>> > > >> > virObjectUnlock(srv);
>> > > >> > return 0;
>> > > >> > --
>> > > >> > 2.13.6
>> > > >>
>> > > >> After thinking again it probably makes more sense (and the code more
>> > > >> beautiful) to initialize the worker pool even for maxworker=0 (within
>> > > >
>> > > > I don't understand why should we do that.
>> > >
>> > > Because right now there are several functionalities broken. Segmentation
>> > > faults in virNetServerGet/SetThreadPoolParameters, it’s not possible to
>> > > start with maxworkers=0 and then change it at runtime via
>> >
>> > Naturally, since no workers means noone to process the request, that is IMHO
>> > the expected behaviour.
>>
>> Yes, a daemon should either run with no workers, or should run with
>> 1 or more workers. It is not value to change between these two modes.
>>
>> So if there's a codepath that lets you change from 0 -> 1 workers,
>> or the reverse, we should make sure that reports an error.
>>
>> Essentially workers=0 is only intended for things like virtlockd
>> or virlogd which don't need to be multithreaded, or indeed must
>> *never* be multithreaded to avoid tickling kernel bugs like
>> virtlockd did in the past.
>
> Also note that workers=0 will cause libvirtd to deadlock, because
> the QEMU driver (and others too) assume that they run in a seperate
> thread from the main event loop.
Yep, I know. What is your preferred way to avoid this?
>
> Regards,
> Daniel
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--
Beste Grüße / Kind regards
Marc Hartmayer
IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
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