Leaking plh_return_segs in containerized pNFS client?

[Omar Sandoval <osandov@osandov.com>]

Hi, Trond,

I'm investigating an issue on our systems that are running your latest
containerized NFS client teardown patches while Jeff is out. We're not
seeing the NFS client get stuck anymore, but I'm debugging what appears
to be a reference leak.

Jeff noticed that there are some lingering network namespaces not in use
by any processes after the container shutdown. I chased these references
through:

   net -> nfs_client -> nfs4_pnfs_ds -> nfs4_ff_layout_ds ->
   nfs4_ff_layout_mirror -> nfs4_ff_layout_segment

What I'm seeing is:

* The nfs4_ff_layout_segment/pnfs_layout_segment has a pls_refcount of
  0, but hasn't been freed.
* Its pls_layout has already been freed, and the nfs_inode
  and nfs_server are also long gone.
* The segment was on pls_layout_hdr->plh_return_segs.

    >>> lseg
    *(struct pnfs_layout_segment *)0xffff88813147ca00 = {
            .pls_list = (struct list_head){
                    .next = (struct list_head *)0xffff8885d49e0f38,
                    .prev = (struct list_head *)0xffff888dee919f80,
            },
            .pls_lc_list = (struct list_head){
                    .next = (struct list_head *)0xffff88813147ca10,
                    .prev = (struct list_head *)0xffff88813147ca10,
            },
            .pls_commits = (struct list_head){
                    .next = (struct list_head *)0xffff88813147ca20,
                    .prev = (struct list_head *)0xffff88813147ca20,
            },
            .pls_range = (struct pnfs_layout_range){
                    .iomode = (u32)1,
                    .offset = (u64)0,
                    .length = (u64)18446744073709551615,
            },
            .pls_refcount = (refcount_t){
                    .refs = (atomic_t){
                            .counter = (int)0,
                    },
            },
            .pls_seq = (u32)2,
            .pls_flags = (unsigned long)10,
            .pls_layout = (struct pnfs_layout_hdr *)0xffff8885d49e0f00,
    }
    >>> decode_enum_type_flags(lseg.pls_flags, prog["NFS_LSEG_VALID"].type_)
    'NFS_LSEG_ROC|NFS_LSEG_LAYOUTRETURN'
    >>> lseg.pls_list.next == lseg.pls_layout.plh_return_segs.address_of_()
    True

So my guess is that there were still segments on plh_return_segs when
the pnfs_layout_hdr was freed. I wasn't able to make sense of how the
lifetime of that list is supposed to work. My next step is to test with
WARN_ONCE(!list_empty(&lo->plh_return_segs)) in the free path of
pnfs_put_layout_hdr(). In the meantime, do you have any ideas?

Thanks,
Omar

P.S. I spotted a separate issue that nfs4_data_server_cache is only
keyed on the socket address, not taking the network namespace into
account, which can result in connections being shared between
containers. This leak has a knock-on effect of pinning dead DS
connections in the cache, which other containers may try to reuse. Maybe
the cache should be split up by netns?