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

On Tue, Jun 19, 2018 at 05:18:17PM +0200, Marc Hartmayer wrote: > On Tue, Jun 19, 2018 at 04:55 PM +0200, "Daniel P. Berrangé" <berrange(a)redhat.com&gt; 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. > > Okay. > > > > > 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. > > virThreadPoolSetParameters allows this change... Does it make sense to > you to allow an empty thread pool (just to keep the values) but to > prohibit a change from 0 -> i workers (i != 0) (and the reverse)? The > condition in virNetServerDispatchNewMessage would be something like 'if > (virThreadPoolGetMaxWorkers(srv->workers) > 0) {' instead of 'if > (srv->workers)'. If yes, this would, IMHO, simplify the code paths and > would be much safer against null pointer dereferencing. virThreadPoolSetParameters should immediately return an error if the caller tries to switch between 0 and non-zero in either direction.

Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|