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

  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.

-- 
Gleb Smirnoff