Re: What's going on with vnets and epairs w/ addresses?

On Tue, Dec 20, 2022 at 08:50:09PM +0000, Bjoern A. Zeeb wrote:
> On Tue, 20 Dec 2022, Mark Johnston wrote:
> 
> > On Sun, Dec 18, 2022 at 10:52:58AM -0600, Kyle Evans wrote:
> >> On Sat, Dec 17, 2022 at 11:22 AM Gleb Smirnoff <glebius@freebsd.org> wrote:
> >>>
> >>>   Zhenlei,
> >>>
> >>> On Fri, Dec 16, 2022 at 06:30:57PM +0800, Zhenlei Huang wrote:
> >>> Z> I managed to repeat this issue on CURRENT/14 with this small snip:
> >>> Z>
> >>> Z> -------------------------------------------
> >>> Z> #!/bin/sh
> >>> Z>
> >>> Z> # test jail name
> >>> Z> n="test_ref_leak"
> >>> Z>
> >>> Z> jail -c name=$n path=/ vnet persist
> >>> Z> # The following line trigger jail pr_ref leak
> >>> Z> jexec $n ifconfig lo0 inet 127.0.0.1/8
> >>> Z>
> >>> Z> jail -R $n
> >>> Z>
> >>> Z> # wait a moment
> >>> Z> sleep 1
> >>> Z>
> >>> Z> jls -j $n
> >>> Z>
> >>> Z> After DDB debugging and tracing , it seems that is triggered by a combine of [1] and [2]
> >>> Z>
> >>> Z> [1] https://reviews.freebsd.org/rGfec8a8c7cbe4384c7e61d376f3aa5be5ac895915 <https://reviews.freebsd.org/rGfec8a8c7cbe4384c7e61d376f3aa5be5ac895915>
> >>> Z> [2] https://reviews.freebsd.org/rGeb93b99d698674e3b1cc7139fda98e2b175b8c5b <https://reviews.freebsd.org/rGeb93b99d698674e3b1cc7139fda98e2b175b8c5b>
> >>> Z>
> >>> Z>
> >>> Z> In [1] the per-VNET uma zone is shared with the global one.
> >>> Z> `pcbinfo->ipi_zone = pcbstor->ips_zone;`
> >>> Z>
> >>> Z> In [2] unref `inp->inp_cred` is deferred called in inpcb_dtor() by uma_zfree_smr() .
> >>> Z>
> >>> Z> Unfortunately inps freed by uma_zfree_smr() are cached and inpcb_dtor() is not called immediately ,
> >>> Z> thus leaking `inp->inp_cred` ref and hence `prison->pr_ref`.
> >>> Z>
> >>> Z> And it is also not possible to free up the cache by per-VNET SYSUNINIT tcp_destroy / udp_destroy / rip_destroy.
> >>>
> >>> This is known issue and I'd prefer not to call it a problem. The "leak" of a jail
> >>> happens only if machine is idle wrt the networking activity.
> >>>
> >>> Getting back to the problem that started this thread - the epair(4)s not immediately
> >>> popping back to prison0. IMHO, the problem again lies in the design of if_vmove and
> >>> epair(4) in particular. The if_vmove shall not exist, instead we should do a full
> >>> if_attach() and if_detach(). The state of an ifnet when it undergoes if_vmove doesn't
> >>> carry any useful information. With Alexander melifaro@ we discussed better options
> >>> for creating or attaching interfaces to jails that if_vmove. Until they are ready
> >>> the most easy workaround to deal with annoying epair(4) come back problem is to
> >>> remove it manually before destroying a jail, like I did in 80fc25025ff.
> >>>
> >>
> >> It still behaved much better prior to eb93b99d6986, which you and Mark
> >> were going to work on a solution for to allow the cred "leak" to close
> >> up much more quickly. CC markj@, since I think it's been six months
> >> since the last time I inquired about it, making this a good time to do
> >> it again...
> >
> > I spent some time trying to see if we could fix this in UMA/SMR and
> > talked to Jeff about it a bit.  At this point I don't think it's the
> > right approach, at least for now.  Really we have a composability
> > problem where different layers are using different techniques to signal
> > that they're done with a particular piece of memory, and they just
> > aren't compatible.
> >
> > One thing I tried is to implement a UMA function which walks over all
> > SMR zones and synchronizes all cached items (so that their destructors
> > are called).  This is really expensive, at minimum it has to bind to all
> 
> A semi-unrelated question -- do we have any documentation around SMR
> in the tree which is not in subr_smr.c?
> 
> (I have to admit I find it highly confusing that the acronym is more
> easily found as "Shingled Magnetic Recording (SMR)" in a different
> header file).

Sorry for the delayed reply, I was travelling for a few weeks and still
haven't caught up.  I did at least write a man page which notes the
multiple meanings of that acronym. :)

Comments and feedback are welcome: https://reviews.freebsd.org/D38108