Re: [Qemu-devel] [PATCH v6 0/7] Rework vhost memory region updates

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Michael S. Tsirkin (mst@redhat.com) wrote:
> On Tue, Jan 16, 2018 at 06:04:01PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > Hi,
> >   This patch set reworks the way the vhost code handles changes in
> > physical address space layout that came from a discussion with Igor.
> > 
> > Its intention is to simplify a lot of the update code,
> > and to make it easier for the postcopy+shared code to
> > do the hugepage alignments that are needed.
> > 
> > Instead of inserting/removing each section during the add/del
> > callbacks of the listener, we start afresh and build a list
> > from the add and nop callbacks, then at the end compare the list
> > we've built with the exisiting list.
> > 
> > v6
> >   Tidy ups from Igor
> >   The biggest change is moving the 'Move log_dirty check' to be
> >   the last patch in the set.
> > 
> > Dr. David Alan Gilbert (7):
> >   vhost: Build temporary section list and deref after commit
> >   vhost: Simplify ring verification checks
> >   vhost: Merge sections added to temporary list
> >   vhost: Regenerate region list from changed sections list
> >   vhost: Clean out old vhost_set_memory and friends
> >   vhost: Merge and delete unused callbacks
> >   vhost: Move log_dirty check
> > 
> >  hw/virtio/trace-events    |   6 +
> >  hw/virtio/vhost.c         | 497 ++++++++++++++++------------------------------
> >  include/hw/virtio/vhost.h |   5 +-
> >  3 files changed, 180 insertions(+), 328 deletions(-)
> 
> 
> Seems to trigger errors with clang runtime sanitizer:
> 
> /scm/qemu/hw/virtio/vhost.c:425:26: runtime error: null pointer passed as argument 1, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:45: runtime error: null pointer passed as argument 2, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:26: runtime error: null pointer passed as argument 1, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:45: runtime error: null pointer passed as argument 2, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:26: runtime error: null pointer passed as argument 1, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:45: runtime error: null pointer passed as argument 2, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:26: runtime error: null pointer passed as argument 1, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here
> /scm/qemu/hw/virtio/vhost.c:425:45: runtime error: null pointer passed as argument 2, which is declared to never be null
> /usr/include/string.h:64:33: note: nonnull attribute specified here


How are you running that test? Can you add this printf and tell me what
it's seeing?

        /* Same size, lets check the contents */
        fprintf(stderr, "%s: %p %p %d\n", __func__, dev->mem_sections, old_sections, n_old_sections);
        changed = memcmp(dev->mem_sections, old_sections,
                         n_old_sections * sizeof(old_sections[0])) != 0;

I'm seeing a bunch of calls where both pointers are NULL, but
n_old_sections is 0, which feels legal to me.

I guess we could make it:
   changed = n_old_sections ? memcmp(....) : false;
just to shut clang up.

Dave

> 
> 
> > -- 
> > 2.14.3
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK