Multichannel mount failures to Samba depending on IP address (single channel works)

[Steve French <smfrench@gmail.com>]

Saw an interesting multichannel failure scenario to Samba today:

Samba server smb.conf has
   "server multi channel support = yes"
in the [global] section but it does not include a line for
"interfaces" (uses the default)

On localhost, mounting to current Samba from Linux (tried various
versions of cifs.ko so does not appear to be a recent regression),
noticed:

1) mount -t cifs //locahost/share /mnt                                    worked
2) mount -t cifs //localhost/share /mnt -o multichannel          failed
3) mount -t cifs //127.0.0.1/share /mnt                                   worked
4) mount -t cifs //127.0.0.1/share /mnt -o multichannel          failed
5) mount -t cifs //192.168.1.190/share /mnt -o multichannel   worked

When mounting with "localhost" or "127.0.0.1" as the server name (non
multichannel) note that it does not show [CONNECTED] in
/proc/fs/cifs/DebugData

Server interfaces: 3 Last updated: 3 seconds ago
1) Speed: 1Gbps
Capabilities: None
IPv4: 192.168.1.198
Weight (cur,total): (0,1)
Allocated channels: 0

2) Speed: 1Gbps
Capabilities: None
IPv6: 2603:8080:2200:13fc:c82b:b16f:52c8:2329
Weight (cur,total): (0,1)
Allocated channels: 0

3) Speed: 1Gbps
Capabilities: None
IPv6: 2603:8080:2200:13fc:5b60:a7d6:77d7:72cc
Weight (cur,total): (0,1)
Allocated channels: 0

Note that when mounting to "192.168.1.190" (non-multichannel) it only
shows two instead of three interfaces (not sure why it drops one of
the IPv6 ones) but it does correctly show [CONNECTED]

Server interfaces: 2 Last updated: 1 seconds ago
1) Speed: 1Gbps
Capabilities: None
IPv4: 192.168.1.198
Weight (cur,total): (1,1)
Allocated channels: 1
[CONNECTED]

2) Speed: 1Gbps
Capabilities: None
IPv6: 2603:8080:2200:13fc:5b60:a7d6:77d7:72cc
Weight (cur,total): (0,1)
Allocated channels: 0

The mount failures with multichannel to 127.0.0.1 are weird - the
first negprot/sessionsetup/tcon works fine but the second negprot then
sessionsetup fails with the server returning with
"STATUS_SESSION_DELETED" which seems strange (since the session is
valid, and channel one session setup worked fine).  Any idea if this
is a Samba server bug?

Presumably the workaround is to add an "interfaces" line to smb.conf
to force it to return 127.0.0.1 as a valid interface, but this still
seems like it could be a server bug.  And quite confusing to users (as
"Resource temporarily unavailable" won't make sense to them since
single channel works fine) Any thoughts?

And log messages are unlikely to help the user figure out the server
config (or bug) issue.

[12421.964837] CIFS: Attempting to mount //localhost/test
[12422.032199] CIFS: VFS: \\localhost Send error in SessSetup = -11
[12422.032234] CIFS: VFS: failed to open extra channel on
iface:192.168.1.198 rc=-11
[12422.137163] CIFS: successfully opened new channel on
iface:2603:8080:2200:13fc:c82b:b16f:52c8:2329
[12422.137401] CIFS: VFS: reconnect tcon failed rc = -11

Thoughts?

-- 
Thanks,

Steve