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.
Regards,
Daniel
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