Linux Virtualization - May 2017 - remove function pointer casts and constify function tables

Probably should have cc'd virtualization at lists.linux-foundation.org too.

On Fri, May 26, 2017 at 11:08:39AM -0400, bfields at fieldses.org
wrote:
> On Tue, May 23, 2017 at 08:23:34AM -0400, bfields at fieldses.org wrote:
> > Unfortunately I can't get anything through testing.  It's not
your
> > patches, it's something in -rc1.  My server VM stops responding to
> > any network traffic randomly in the middle of a run.  If I log in from
a
> > serial console, I see the interface is up and everything looks OK.  I
> > haven't had the chance to do much more, and I'm not sure where
to
> > start....  I started a git-bisect attempt, but there are several
> > unrelated problems, and I'm not sure this one is 100%
reproduceable.
> 
> It looks like it may be due to something pulled in with virtio updates.
> I've reproduced the problem on c8b0d7290657 "s390/virtio: change
> maintainership" but not on v4.11.  Are there any known issues with
those
> commits?
> 
> I've just been doing this long-running bisect while working on other
> stuff.  My reproducer (basically just running a bunch of NFS
> connectathon tests over a variety of protocol versions and security
> flavors) doesn't hit the bug reliably, and I've had to restart a
couple
> times probably due to false negatives.  But this looks pretty promising,
> and there's only 17 commits in that range, so I'll keep bisecting.
> 
> --b.

Looks like the culprit is very likely d85b758f72b0 "virtio_net: fix
support for small rings".

After that patch, my NFS server VM stops responding to packets after a
few minutes of testing.  Before that patch, my server keeps working.

--b.

On Fri, May 26, 2017 at 03:31:33PM -0400, bfields at fieldses.org
wrote:
> Looks like the culprit is very likely d85b758f72b0 "virtio_net: fix
> support for small rings".
> 
> After that patch, my NFS server VM stops responding to packets after a
> few minutes of testing.  Before that patch, my server keeps working.
> 
> --b.
Others complained about that too.
I'm still trying to reproduce though.

Meanwhile, could you please locate this line of code:
+               vi->rq[i].min_buf_len = mergeable_min_buf_len(vi,
vi->rq[i].vq);

and add something like
        printk(KERN_ERR, "min buf = 0x%x expected 0x%x size 0x%x big
%d\n",
               vi->rq[i].min_buf_len, GOOD_PACKET_LEN,
               virtqueue_get_vring_size(vi->rq[i].vq),
               (int)vi->big_packets);

after it?
Then boot and capture the output.

Thanks!


-- 
MST

On Fri, May 26, 2017 at 03:31:33PM -0400, bfields at fieldses.org
wrote:
> Looks like the culprit is very likely d85b758f72b0 "virtio_net: fix
> support for small rings".
> 
> After that patch, my NFS server VM stops responding to packets after a
> few minutes of testing.  Before that patch, my server keeps working.
> 
> --b.

So I think I know what caused this: looks like some hypervisors
aren't prepared to deal with a situation where packet size
becomes very small.

But which hypervisors exactly? I'd like to know in order to detect these
and decide whether I blacklist bad ones or whitelist known-good ones.

Thanks!

-- 
MST