Re: [libvirt] [PATCH 2/2] rpc: Fix segmentation fault when no worker pool is available

On Tue, Jun 19, 2018 at 05:03 PM +0200, "Daniel P. Berrangé" <berrange(a)redhat.com&gt; 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(a)redhat.com&gt; 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(a)linux.ibm.com&gt; 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(a)linux.ibm.com&gt; >> > > >> > Reviewed-by: Boris Fiuczynski <fiuczy(a)linux.ibm.com&gt; >> > > >> > --- >> > > >> > 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. Shall we then disallow this value for the option "max_workers" in libvirtd.conf?