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Re: [libvirt] [PATCH 01/10] util: Introduce thread queues



On Fri, May 22, 2015 at 10:16:26 -0400, John Ferlan wrote:
> 
> 
> On 05/21/2015 06:42 PM, Jiri Denemark wrote:
> > Our usage of pthread conditions does not allow a single thread to wait
> > for several events from different sources. This is because the condition
> > is bound to the source of the event. We can invert the usage by giving
> > each thread its own condition and providing APIs for registering this
> > thread condition with several sources. Each of the sources can then
> > signal the thread condition.
> > 
> > Thread queues also support several threads to be registered with a
> > single event source, which can either wakeup all waiting threads or just
> > the first one.
> > 
> > Signed-off-by: Jiri Denemark <jdenemar redhat com>
> > ---
> >  po/POTFILES.in            |   1 +
> >  src/Makefile.am           |   2 +
> >  src/libvirt_private.syms  |  15 ++
> >  src/util/virthreadqueue.c | 343 ++++++++++++++++++++++++++++++++++++++++++++++
> >  src/util/virthreadqueue.h |  54 ++++++++
> >  5 files changed, 415 insertions(+)
> >  create mode 100644 src/util/virthreadqueue.c
> >  create mode 100644 src/util/virthreadqueue.h
> > 
> 
> Ran the series through Coverity and came back with this gem
> 
> > +
> > +void
> > +virThreadQueueFree(virThreadQueuePtr queue)
> > +{
> > +    if (!queue)
> > +        return;
> > +
> > +    while (queue->head)
> > +        virThreadQueueRemove(queue, queue->head);
> 
> (3) Event cond_true: 	Condition "queue->head", taking true branch
> (6) Event loop_begin: 	Jumped back to beginning of loop
> (7) Event cond_true: 	Condition "queue->head", taking true branch
> 
> 283  	    while (queue->head)
> 
> (4) Event freed_arg: 	"virThreadQueueRemove" frees "queue->head". [details]
> (5) Event loop: 	Jumping back to the beginning of the loop
> (8) Event deref_arg: 	Calling "virThreadQueueRemove" dereferences freed pointer "queue->head". [details]
> 
> 284  	        virThreadQueueRemove(queue, queue->head);

False positive. If virThreadQueueRemove frees queue->head, it also
updates it with queue->head->next.

Jirka


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