cifs share hangs after several hours

[Phil Tull]

I have 2 cifs shares from Ubuntu to a Windows 2012 NAS.
The shares work at first, then after a few hours, one or both hang and do not respond until rebooting the ubuntu server.
In my example below, the video share has hung, but music is still working. This system did work last year before I upgraded packages to 14.04.1.
I have tried purging and reinstalling cifs-utils, but no improvement.

This is /etc/fstab:
//deepthought/video$ /mnt/video cifs ro,_netdev,username=plex,password=xx,sec=ntlm 0 0
//deepthought/music$ /mnt/music cifs ro,_netdev,username=plex,password=xx,sec=ntlm 0 0

This is the output from /proc/fs/cifs/DebugData:

Display Internal CIFS Data Structures for Debugging
---------------------------------------------------
CIFS Version 2.02
Features: dfs fscache lanman posix spnego xattr acl
Active VFS Requests: 2
Servers:
1) Name: 192.168.0.213 Domain: AQUILA Uses: 1 OS: Windows Server 2012 R2 Datacenter 9600
        NOS: Windows Server 2012 R2 Datacenter 6.3 Capability: 0x1e3fc
        SMB session status: 1 TCP status: 1
        Local Users To Server: 1 SecMode: 0x3 Req On Wire: 0
        Shares:
        1) \\deepthought\music$ Mounts: 1 Type: NTFS DevInfo: 0x20020 Attributes: 0xc700ff
        PathComponentMax: 255 Status: 0x1 type: DISK

        MIDs:

2) Name: 192.168.0.213 Domain: AQUILA Uses: 1 OS: Windows Server 2012 R2 Datacenter 9600
        NOS: Windows Server 2012 R2 Datacenter 6.3 Capability: 0x1e3fc
        SMB session status: 1 TCP status: 4
        Local Users To Server: 1 SecMode: 0x3 Req On Wire: 1
        Shares:
        1) \\deepthought\video$ Mounts: 1 Type: NTFS DevInfo: 0x20020 Attributes: 0xc700ff
        PathComponentMax: 255 Status: 0x1 type: DISK DISCONNECTED

        MIDs:
        State: 2 com: 114 pid: 11739 cbdata: ffff8800e515c800 mid 11

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: cifs-utils 2:6.0-1ubuntu2
ProcVersionSignature: Ubuntu 3.13.0-37.64-generic 3.13.11.7
Uname: Linux 3.13.0-37-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
Date: Tue Oct 14 17:23:14 2014
InstallationDate: Installed on 2014-03-06 (222 days ago)
InstallationMedia: Ubuntu-Server 12.04.4 LTS "Precise Pangolin" - Release amd64 (20140204)
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: cifs-utils
UpgradeStatus: Upgraded to trusty on 2014-08-22 (53 days ago)

[Phil Tull (puil)]

Update: I found that the hanged share does respond but it takes about an hour.
In other words, I can enter "ls /mnt/music" and after about an hour it will list the directory.
After a reboot it is back to normal for a few hours.

[Phil Tull (puil)]

I just made an even more interesting discovery.
I timed how long it takes to do a directory.
# time ls /mnt/music

It takes EXACTLY 15 minutes 31 seconds to list the folder.
This is repeatable.

Note: it normally takes 0.015s to list the folder.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.